Fish books. Books on fishes.Books on fishkeeping


Author: Jennings, Gerald (Gerald Jennings)

The Cyclic Chemistry of Marine Aquaria
Basic Guide to the Chemistry of keeping marine aquaria and biosystems in non-technical terminology.

Date first published: 2004
Publication: Calypso Publications, London
Reprinted from Aquarticles:

Full credits must be given in any non-commercial reproduction. Commercial reproduction is not allowed.


Basic Guide to the Chemistry of

Marine Aquariums

The Cyclic Chemistry of Marine Aquaria and Biosystems

A Guide as to why your marine system can go wrong and where it

can go wrong, and possibly what to do to stop it going wrong.

It makes sense to buy this book before losing or killing expensive

marine fishes

ISBN 0 906301 03 3 2003

Calypso Publications. If you want to copy bits of the text, or even the whole text itself, then we only mind if you do not ask

and do not give credits – so be polite and ask. Courtesy costs nothing.

Calypso Publications.

Other Related Calypso Titles include:

Synthetic Seawaters for Laboratories and Aquaria

ISBN: 0 906301 009

A History of Tropical Marine Fishkeeping in the U.K. 1960-1980

ISBN: 0 906301 99 8


Every year hundreds of thousands of marine fishes die as a result of ignorance.

Many of these are newly acquired pets whose loving and caring owners

unintentionally manage to terminate their lives ironically whilst trying to give

them the best life possible.

There has always been little support they could call on. The trade in animals is,

like any other trade, a cash cow, and few sellers will accept any responsibility

once the purchased have left their care.

The “organized hobby” is now virtually toothless and non-existent – no longer are

there many local experts and aquarium groups to turn to – and their successor, the

internet, is both impersonal and generally overly well stocked with rather poor

advice. There are always exceptions of course.

The IFOCAS group is such an exception. It is dedicated to spreading accurate and

wherever possible,free information, on fishkeeping worldwide.

IFOCAS have sponsored us in publishing this booklet which it is hoped will convey

at least a little light in to the often murky waters of fishtank chemistry. W have

tried to simplify a very technical subject so we ask the purists not to be

offended. We are also able to offer free helplines for all enquiries on this

matter, both simple and technical – just use one of the websites or email

addresses listed below.

Calypso Publications. http://

IFOCAS. The International Federation of Online Clubs and Aquatic Societies

IFOCAS is represented in all Continents


A marine aquarium is an unnatural environment. In the sea, water conditions are basically

constant, but in an aquarium water conditions are continually changing. Since aquatic

organisms are in intimate contact with their environment, any change in the composition of

the water has a profound effect on their well - being.

As an aquarist you must be able to recognize the condition of the water in your aquarium,

and take appropriate action when water quality declines, as it inevitably will. Acquiring a

basic understanding of water chemistry is an important step in becoming a more

knowledgeable and, ultimately, a more successful marine aquarist.

It is possible to maintain and enjoy a marine aquarium with little or no concern for routine

water analyses. In fact, many hobbyists are content with knowing that regular, partial water

changes are sufficient to maintain adequate water quality in many situations. As long as such

aquariums are not overcrowded or overfed, there is little reason to expect that water quality

will deteriorate enough to be detrimental.

However, many marine enthusiasts are not content with simply maintaining decorative

displays. Some are challenged to maintain particularly delicate fish and invertebrates. Others

are spawning and rearing many popular species.

These aquarists need to know more about the water in their systems. Analysis of the water

can greatly complement the information gained by careful observation of the aquarium inhabitants,

and help establish guidelines for all future aquarists.

Seawater is a complex solution, and to accurately determine the concentrations of many

components is difficult, time consuming, and costly. Fortunately, experience has shown that

we can learn a great deal about aquarium environments by analyzing for a relatively small

number of items.

Unfortunately, the marine aquarist wishing to consider water chemistry is often in an

uncomfortable position. Bits and pieces of information are frequently gathered from various

sources that can be both contradictory and inadequate.

This text attempts to fill some possible gaps in the reader's knowledge of water chemistry. It

discusses the nature of seawater, and common water chemistry parameters with emphasis on

the type and value of the information that can be obtained from a particular analysis.

To aid in understanding the following chapters, it is appropriate to define several terms

before continuing. Additional definitions are also found in the glossary towards the end.

A little basic chemistry………..

The basic chemical unit is the atom. It is composed of three distinct small particles - protons,

neutrons, and electrons

( The number of protons equals the number of electrons, and the identity of the atom is

defined by the number of protons.)

Atoms are usually expressed in text as chemical symbols.

For example, Ca stands for calcium, and H stands for hydrogen.

Other symbols are based on Latin names, such as Na for sodium

(Natrium) and K for potassium (Kalium).

Symbols are convenient and will be used frequently in the following text. Some of the

commonly used symbols are shown below:

Common Chemicals and Symbols used

Hydrogen H Manganese Mn Silicon Si

Lithium Li Iron Fe Nitrogen N

Sodium Na Cobalt Co Phosphorous P

Potassium K Nickel Ni Oxygen 0

Rubidium Rb Copper Cu Sulphur S

Magnesium Mg Zinc Zn Fluorine F

Calcium Ca Boron B Chlorine Cl

Strontium Sr Aluminium Al Bromine Br

Barium Ba Carbon C Iodine I

Vanadium V

A collection of identical atoms is called an element. For example, sodium is an element. A

piece of pure sodium consists of only sodium atoms, and they cannot be changed to atoms of

any other elements. They will always be sodium atoms. However, they are capable of

reacting or combining with atoms of other elements to form new materials called molecules.

A molecule is a collection of two or more different types of atoms connected by chemical


(If sodium, a soft, silvery metal, reacts with chlorine, a greenish-yellow gas, sodium chloride (common salt), is

formed. The substance formed is not similar to either of the components.)

Ions are electrically charged particles. They possess an excess of electrons (negatively

charged) or a deficiency of electrons (positively charged). Some molecules form ions when

they are dissolved in water.

Sodium chloride (NaCl), dissolved in water, produces positively charged sodium ions (Na+)

and negatively charged chloride ions (Cl-)

(a) A Sodium chloride molecule forms a positively charged sodium ion and a negatively

charged chloride ion.


(b) A Potassium nitrate molecule forms a positively charged potassium ion and a

negatively charged nitrate ion.

Ions can be either atoms, like sodium, potassium and chloride, or molecules, like nitrate

If both sodium chloride and potassium nitrate are dissolved in the same solution, it is

impossible to tell what the original compounds were. Dissolving potassium chloride and

sodium nitrate produces the same result). It is often difficult to represent the components of

complex solutions as neutral (uncharged) compounds. For this reason, the composition of

natural seawater is given by concentrations of elements, such as sodium and magnesium,

or ions, such as nitrate, rather than as concentrations of compounds, such as sodium

chloride, magnesium sulphate, or sodium nitrate, so identical solutions can be obtained by

dissolving various combinations of different compounds.



Elements or molecules in seawater are usually shown as concentrations by

volume or weight in solution. Modern literature uses the metric units of

weight per volume, milligrams per liter (mg/l). Parts per million (ppm) is

more popular in non-technical literature. The two terms, although different,

are often used interchangeably.

Many elements occur in solution as free ions, such as sodium (Na+) or

chloride (Cl-); and it is convenient to simply report the concentrations of the

elements (e.g., 10,500 mg/l Na+).

Other elements occur as components of molecular ions, such as nitrate (NO3-

) or phosphate (PO4--); and it is more convenient to report concentrations in

terms of the element of interest.

For ammonia (NH3), nitrite (NO2-), and nitrate (NO3-), concentrations are

reported as milligrams per litre of ammonia-nitrogen .(NH3-N), nitritenitrogen

(NO2--N). and nitrate-nitrogen (NO3--N). Similarly, for phosphate,

phosphorous is reported (P04--P).

This system permits easy, direct conversion. For example, 10 mg/l NH3-N

will produce 10 mg/l NO2--N and ultimately 10 mg/l NO3--N. When reading

other books or articles, it is important to know which system is in use. To

convert mg/l NH3-N to mg/l NH3, multiply by 1.3; to convert mg/l NO2--N to

mg/l N02-(ion), multiply by 3.3; to convert mg/l NO3--N to mg/l NO3-(ion),

multiply by 4.4.

Numbers in the latter system are always higher because they take in to

consideration the contribution of the hydrogen and oxygen to the molecular

weight. For example, 10 mg/l nitrite-nitrogen equals 33 mg/l nitrite ion, but

both numbers represent the same concentration of nitrite. It's similar to your

thermometer saying that the temperature is 75 degrees Fahrenheit or 25

degrees Celsius. You know that, although the numbers are different, the

temperature is still virtually the same.

The Seawater Itself

(A.) Natural Seawaters

Seawater is a solution containing approximately 34 parts per thousand of dissolved

materials. Many oceanographers have conducted determinations of the composition of

seawater throughout the world and all results are extremely constant with only a few wellknown

area exceptions.

An examination of record tables shows that seawater contains most chemical elements, many

at extremely low concentrations. However, in our discussion of aquarium water chemistry,

only a few of these elements are critically important.


The major ionic components of seawater are the same as the ions responsible for maintaining

electrical and osmotic balance within the cells

of living animals andfor transmission of nerve impulses.

The complete absence of any one of these major ions is fatal. A fish placed into a modified

seawater solution that contained no potassium would soon die as a result of the chemical

imbalance within the animal.

The “Biggest Six” Major Ions Found In Seawater

Component Concentration


Chloride 19,000

Sodium 10,500

Sulphate 2,600

Magnesium 1,350

Calcium 400

Potassium 380

The major components vary little. It is accepted practice to represent these as either ratios to

chlorinity.** or milligrams per litre as shown above

** Chlorinity. For definition see glossary.

The ratios for nine major ions are listed below together with any natural variations.

Sodium. (Na+ ) .556+/-0 .0003

Calcium.(Ca++) .0210+/-.0005

Magnesium. (Mg++) .06?l+/-.0005

Potassium. (K+) .O2OO+/-.0005

Strontium. (Sr++) .00060+/-.00015

Chlorine as chloride (Cl-) 1.0

Sulphur as sulphate (SO4) 1395+/-0005

Bromine as bromide, (Br) 00~3+/-.0001

Boron as H3BO3. 00134+/-.00005

(Bicarbonate, carbonate & C02 contents are variable. )

The above ratios are all taken from modern analyses. Older figures may differ.

There are very few natural exceptions to the above ratios, and most of these when they occur

are extremely localised. Those that may be of significance are :

Magnesium: Slightly higher ratios are recorded for the Gulf of Aden and the eastern

Mediterranean, being .0681 and .0688 respectively.

Calcium: Most records prior to about 1938 have to be recalculated as they include Strontium


Strontium: (See remark on calcium above). Strontium is used by many radiolarians and is

heavily adsorbed by diatoms and red and green algae.

Boron: Ratios increase in the deep Pacific and may exceed .00162 It is used by many

marine plants and contributes to the basicity discussed later under pH

The major ions are an area of little concern to most fully marine, as opposed to brackishwater

aquarists. Preparations of synthetic seawater always attempt to duplicate the

concentrations of the major ions of natural seawater, and this can be accomplished with

many different combinations or recipes of chemical compounds. Since the major ions can be

obtained from readily available chemical raw materials, it is probably safe to assume that all

commercial formulations of synthetic sea salts have succeeded in duplicating, at least, this

part of the sea.


The minor ions present in seawater exert an influence far greater than their concentrations

suggest. They represent less than half of one percent of the total, most of which is silicate or

fluoride and vary considerably from season to season and area to area. Of the 67 so far

identified approximately 24 are either known or thought to be of some biological importance.

Of the remaining 33 little information is available, save for the occasional research paper,

though it is known that some occur in remarkably stable concentrations in all open ocean

waters. Six of these are included in a table later in addition to the eighteen of biological

interest listed. Much more research into other microconstituents is needed.

As has already been mentioned the concentrations of some of these traces do vary (for a number of

reasons), and this has to be taken into consideration in any assessment of water condition. Most earlier

types of synthetic waters were based on minor constituent readings taken from waters around the

coasts of temperate continents, and are not accurate for the central areas of larger water masses- these

being in general much poorer in nutrients such as phosphate, nitrate and iron than their continental





Antimony Dysprosium

Fluorine Beryllium Erbium

Nitrogen (N03 ) Bismuth Europaeum

Lithium Cadmium Gadolineum

Rubidium Caesium Hafnium

Iodine Cerium Holmium

Phosphorus (PO4) Chromium Lutetium

Barium Gallium Neodymium

Iron Germanium Praesodymium

Molybdenum Indium Protoactinium

Zinc Lanthanum Rhenium

Selenium Krypton Samarium

Manganese Lead Terbium

Vanadium Mercury Tantalum

Nickel Radium Ytterbium

Uranium Ruthenium

Aluminium Silver

Arsenic Thallium Argon

Copper Thorium Deuterium

Cobalt Tin Helium

Niobium Titanium Neon

Yttrium Tungsten Radon

B12 Zirconium


Some microconstituents, notably nitrate, nitrite and ammonia, which occur naturally in ocean

waters, are probably unnecessary additions to any synthetic formulation, unless it is to be

used solely for plants and algae. These are formed quite quickly in waters by the metabolic

activity of higher animals, and indeed this process can cause dangers in small closed circuit

systems. It is notable that open ocean waters and tropical reef waters seem to contain much

less. Results have been published -some very recently- on the following relationships.

Lithium-Rubidium, Strontium-Calcium, Phosphate-Arsenate, Copper – Zinc, and many

more, a full list of which is not practicable here.

Some of the ratios are of greater importance than others and are useful in the comparison of



If in addition to its salinity and temperature (from which its SG -or specific gravity can be

calculated) the pH is known, then its content of bicarbonate, carbonate, molecular carbon

dioxide & total carbon dioxide can be calculated. (NB. This does not apply to synthetic formulations) The

total carbon dioxide present in solution varies almost in direct proportion to salinity If 35

parts per thousand water at 15 deg. C. is brought into equilibrium with the atmosphere it

will show a pH of about 8.16, which is increased by the growth of any plants and decreased

by the respiration of animals.

Bicarbonate is most important because it is the ion primarily responsible for buffering, or

maintenance of pH. Borate also provides some contribution to the buffer system, but its effect

in natural waters is small in comparison. (The subject of pH will be discussed in a subsequent


The importance of the remaining minor ions is less obvious. Silicate is essential to certain

algae, and perhaps some animals. Bromide and Strontium, however, have more complex

relationships . It is likely that the complete absence of either would have little effect on the

health of most, but not all, aquatic organisms.

Trace elements

Trace elements are those ions that are normally encountered at concentrations near or below

1.0 mg/l

The term trace element refers only to the fact that the element is present in trace quantities.

The term as applied does not itself imply any degree of importance with regard to the health

of aquatic organisms.

Many aquarists fail to differentiate between trace elements and essential elements. They are

two distinct groups. Not all trace elements are essential, though the long-term absence of

some within a system has yet to be assessed

Trace Elements

There is no biological process that depends on the presence of all of those above. Even

though they are trace elements normally encountered in natural ocean water, they are

probably not essential elements. Many trace elements are not essential chemical elements

according to present-day information.

Many of the trace elements that are essential are heavy metals (e.g., Chromium, Manganese,

Iron, Cobalt, Copper, and Zinc). Their importance to living organisms depends on the ability

to interact with various organic molecules, such as enzymes, and form stable complexes with

specific biological functions.

Water in an established aquarium contains significant quantities of dissolved compounds

that may also be capable of forming stable complexes that make the metallic elements

unavailable. Additionally, these complexes are readily removed from solution by activated

carbon and other adsorbents.

Even in the absence of organic molecules and adsorbents, these elements may form insoluble




Silicon (1) 500-2,900

Fluorine (2) 1,350+/- 50

Nitrogen as N03 (1) 600+/-100

Lithium (2) 170+/- 30

Rubidium (2) 120+/- 10

Iodine (1) 55+/- 10

Phosphorus as P0+ (1) 1 to 90

Barium (1) 6 to 90

Iron (1) 1 to 40

Molybdenum (1) 9 to 16

Zinc (1) 5 to 21

Selenium (2) 5+/- 1

Manganese (1) 0.4 to 10

Vanadium (1) 0.2 to 7

Nickel (1) 0.5 to 6.6

Uranium (2) 2.5 to 3.3

Aluminium (2) 1 to 5

Arsenic (1) 2.4+/- 0.3

Copper (1) 0.9 to 3

Cobalt (1) 0.1 to 0.7

Niobium (1) 0.015

Yttrium (1) 0.01 to 0.3

(1) Components of proven or suspected

biological activity

(2) Components of known ratio stability

Figures given are taken from various published

statistics, and are the latest available for open oceanic

waters unaffected by land drainage or other sources.

The table above is also representative of many tropical

reef waters .

inorganic compounds, such as carbonates, or hydroxides which precipitate from solution. All

these various mechanisms combine to make the aquarium water an unreliable source of

many essential trace elements.

The problem of supplying essential trace elements is not one of water chemistry, it is one of

nutrition. It is reasonable to expect that higher animals should obtain essential nutrients, including

trace elements, from the food they eat. The best method of insuring that your

animals receive these nutrients that they require is to provide a varied diet of high quality


The Seawater Itself

(B) Synthetic Seawaters


The major salts used in formulation correspond approximately to the major constituents of

ocean water shown .to ascertain how large a quantity of salt may be required it is usual

practice to convert the natural readings, into gram-equivalents, from their original grams per

kilo quantities as shown on the Table. This process is best described by giving an example of

the technique.

Column (a) of Table 1 shows the weights of nine final elements required. Gram per kilogram

weights are then divided by the atomic weight of each element concerned to convert them

into gram-equivalent weights. eg;-

The weight of element in seawater divided by the Atomic weight of the same element = the

Gram-Equivalents weight.

Most manufacturers of laboratory chemicals state the molecular weight of a reagent or salt on

its packaging and labels, if not also in their catalogues. A simple multiplication will then

provide a working result as:-

Gram-Equivalent weight x Molecular weight = Final weight of salt needed.

(The mathematics involved also of course work in reverse, and formulae stating weights of

salts can be converted back into weights of elements per kilo and then compared to Table 1.)

It is imperative that if a formula is being worked out, one works in reverse order, dealing

first with the minor constituents, then on up into the major constituents to the penultimate

figure, the one for Sodium chloride. The salt containing bicarbonate is the last to be

calculated, enough HCO ions (theoretically) being added to use any spare sodium ions as

yet unpaired in the formulation , remembering that any ion carrying a positive (+) indicator

has to be paired with a similar ion carrying a (-) negative indicator, and that where an ion

carries two symbols of one type, it requires double the quantity of an opposite type

carrying only one symbol.(eg. Na+ plus C1- = NaCl, which is common salt but Na+ plus SO4--

= Na2SO4 ,or sodium sulphate.

Thus only ten gram equivalents of chlorine (Cl) are needed to neutralise ten gramequivalents

of sodium in the first example but twenty gram-equivalents of sodium would

be used in neutralising ten gram-equivalents of sulphate in the second.


In the preparation of this text we have incorporated as much modern data as possible. The

synthesis of artificial seawater itself dates back some 150 years, and since the voyage of

"HMS Challengerand Ditmar's subsequent publication of its findings formulae have been

proposed that simulate natural seawater.

There are many reasons for wanting to synthetically produce a substance which in nature

covers over seven-tenths of our native planet , but undoubtedly the major one for biologists,

aquarists and aquarium managers everywhere is convenience.

Approximately ninety six percent of seawater is water, only the remainder being salts, and

transportation of any bulk liquid is both tedious and expensive. Even assuming that one is

willing and able to undertake the collection of one/s own seawater there are problems:-

(1) If collected close on-shore it may be polluted - a fact that is often not immediately obvious

but may often result in later losses of stock.

(2) The waters of the European and North Atlantic (or indeed any Continental shelves -

which include most off-shore areas around our coasts) differ in many respects both from

oceanic waters and to those present in tropical seas.

In these times of 'Convenience Products' it is far simpler to think in terms of a 'Convenience

Seawater', - one either made from easily obtainable laboratory chemicals, or pre-package salt

mixes from your local aquarium supply shop. and then - Hey Presto – a breed of “instant

seawater” How good it will be depends entirely on the scrupulousness of the manufacturer.

Is it the nearest possible synthesis, or just a mixture designed to keep things going for a while

For those about to become interested in the field we have included a large number of pages

in the text devoted to various aspects of this discussion and for those dedicated chemists who

wish to construct their own “ perfect seawater” a note – it has already been done. The

formula can be found in one of the Appendices at the rear. Notwithstanding this, we hope

that this book will even appeal to those who are apprehensive even at the mention of the

word chemistry. We make no apologies for its simplicity, and wherever possible it uses non technical

and very easy-to-understand terms. For those already interested we have included

a bibliography.

Way back in 1979 the team at Calypso Research in the UK published what is probably the

definitive work on “Synthetic Seawaters” and keen readers are urged to request a copy from

them if required. The text of their report proper covers an assessment of nine formulae for

synthesizing seawaters. Some of these are old, some are relatively modern, and one is as yet

unpublished in the marine biological paper for which it was intended . All of these nine

formulae are in everyday use , some throughout the world, others only in the U.K. and

Europe. Many of them have been commercially marketed under an assortment of trade

names, either in their original form, or as a modification, Some of the marketed products

have been 'modified' for use in tropical marine aquaria. Where permission has been given

either by precedent or in writing, the names under which the formulae discussed have been

marketed are given in the report text.

The following are some of the trade names under which the examined salts have been

marketed for aquarium use. Legal protection exists in all cases.

'Aqua-Sea', Dr.Axelrod's Formula, 'C-Water', Meereswasser, 'Instant Ocean', Marina,

H.W.Meeressalz , Rila Marine Mix, Reef Salts, 'Synthetica', 'Tropic-Marin', 'Triton Marine

TM Salts',

This list is not comprehensive and not all of these thirteen formulae have been examined,

Feeding in relation to microconstituents

Feeding a variety of foods is the best means of meeting nutritional requirements

Commercial aquarists have realized this for some time, and commercial fish foods contain supplemental

quantities of essential micro-nutrients. This attitude is now being seen at the hobbyist level, and many similar

foods for ornamental fish are now available.

If higher animals are your primary concern, there should be no need to add supplements to the aquarium water.

However, if plants (algae) are a primary interest, the situation is different, because plants do not "eat" and must

obtain their nutrients by direct absorption from the water.

Most aquariums that contain fish are also capable of supporting a modest growth of algae, because the waste

products of the fish provide sufficient nutrients. However, for intensive algae culture, supplements are always

necessary to restore nutrients that have been depleted from solution.

As interest in spawning marine fish grows, intensive algae culture is gaining increasing attention among marine

hobbyists. It often becomes necessary to produce quantities of micro-algaes which are, in turn, used to culture

food for newly hatched larval fish. Useful algal growth supplements are commercially available, or may be

prepared from one of numerous published formulae.

Algae are on the bottom of the food chain in nature; and it is likely that many of the nutrients that they absorb

from solution ultimately supply the higher animals.

The Chemical Environment

If one examines analyses of seawater, two important points are evident. First, proportions of

all the major elements are remarkably consistent throughout the world as has been

demonstrated in previous paragraphs. This is fortunate because it allows us to mix

organisms that are native to many different locations.

Secondly, concentrations of inorganic nutrients (nitrogen as ammonia, nitrite and nitrate, and

phosphorous as phosphate) and dissolved organic matter are quite low. This is a major

chemical difference between seawater in the ocean and seawater in an aquarium.

Accumulations of these inorganic components is a characteristic of closed system aquariums

and must be controlled by proper maintenance and filtration.

The following chapters discuss various water quality parameters that you are capable of

controlling, and, in fact, must control. With a few unsophisticated accessories you can

monitor a-number of important factors and take appropriate action when necessary.


Variations in naturally recorded salinities are small. With the exception of areas such as the

Baltic, which is extremely low in dissolved salt the regions immediately adjacent to melting

polar ice, and certain localities in the Red Sea it rarely exceeds 38 parts per thousand and is

normally not less than 33 parts per thousand. Nine major ions constitute in excess of 90% of

these readings. The salinity value was originally obtained by titration but more modern

estimations are usually made by methods using a range of techniques; electrical

conductivity, its refractive index, density, or the velocity of transmitted sound signals.

Salinity is a measurement that indicates the amount of salts dissolved in water.

Concentrations are commonly expressed as parts per thousand (ppt or 0/00). Normal

seawater salinity is 34 parts per thousand, meaning that 1,000 grams of seawater contains 34

grams of dissolved salts.

Marine aquariums are usually maintained at salinities slightly lower than natural sea water,

commonly 27 to 31 parts per thousand. This lower salinity benefits fish by requiring less

energy to maintain osmotic balance.

Aquarists ordinarily determine salinity indirectly by measuring specific gravity, which is a

comparison of the density of a solution at a specified temperature (usually 1 50C) to the

density of pure water at a specified temperature (usually 40C). A specific gravity of 1.100

means that at 150C, the solution being measured is 1.100 times denser than pure water at 40C.

Changes in the amount of salt dissolved in the water affect the specific gravity in a

predictable and directly related manner. Therefore, every salinity reading will have a

corresponding specific gravity. If the specific gravity is known, the salinity can be found by

using conversion tables.

Specific Gravity (SG) is conveniently measured by use of a hydrometer, Higher specific

gravities cause the indicators to float higher in the solution. - lower specific gravities cause

them to float lower. For ease of use, a hydrometer should be calibrated at a temperature near

that of the water being tested. Most high quality aquarium hydrometers are calibrated for

use at 750F. Hydrometers calibrated at significantly different temperatures, such as 600F,

require corrections to obtain the actual specific gravity.

For most marine aquariums at 750F a reasonable estimate of salinity can be obtained by

taking the last two digits of the specific gravity reading and multiplying by 1.35. (Example:

Specific Gravity 1.020. Multiply 20 x 1.35 = 27 -ppt for estimated salinity).

In actual practice, most hobbyists dispense with the use of salinity and simply refer to the specific

gravity. The range 1.020 to 1.023 is most common.


Most aquarists, freshwater and saltwater alike, begin their education in water chemistry

when they are introduced to pH testing. The earliest aquarists realized the importance of

proper pH, and an understanding of elementary concepts of pH will aid in understanding

subsequent topics. (Keep in mind that pH is a complicated subject and that the following is

greatly simplified).

Principles of pH

Water is composed of two elements, hydrogen and oxygen. In a molecule of water, two

hydrogen atoms are bound to a central oxygen atom (Fig. 5a). In a volume of water, some of

the molecules dissociate, or separate, into hydrogen ions (H+) and hydroxide ions (OH-) The

pH represents the concentration of the hydrogen ions.

Lower numbers on the pH scale represent higher hydrogen ion concentrations, and each pH

unit denotes a tenfold change in concentration. That is, at pH 6, there are 10 times more

hydrogen ions than at pH 7; at pH 8, there are 1/10 the number of hydrogen ions at pH 7.

When the number of hydrogen ions equals the number of hydroxide ions, the hydrogen ion

concentration is represented by pH 7; and the solution is neutral. If the hydrogen ion

concentration is increased, the pH falls below 7, and the solution is acidic. Conversely, if the

hydrogen ion concentration is decreased, the pH rises above 7, and the solution is alkaline.

pH can be changed by addition of substances that affect the hydrogen ion concentration.

Hydrochloric acid (HCl) dissociates into hydrogen ions (H+) and chloride ions (Cl-). When

added to a solution, there will be an increase in the overall hydrogen ion concentration and

pH will drop.

It's easy to visualize that adding more hydrogen ions increases their concentration and

lowers pH, but how is the hydrogen ion concentration lowered to increase pH? Obviously,

one cannot reach into a solution and selectively pull out the hydrogen ions.

The hydrogen ion concentration and the hydroxide ion (OH-) concentration are related.

When one increases, the other decreases. Adding a substance that increases the hydroxide

ion concentration lowers the hydrogen ion concentration. Sodium hydroxide (NaOH)

dissociates into sodium ions (Na+) and hydroxide ions (OH-). Addition to a solution

increases the hydroxide ion concentration and, consequently, decreases the hydrogen ion

concentration, resulting in a higher pH.

Many substances affect pH when added to an aqueous solution. Some contain neither

hydrogen ions nor hydroxide ions, but affect the pH indirectly.

Sodium bicarbonate dissociates into sodium ions (Na+) and bicarbonate ions (HCO3-).

Solutions of sodium bicarbonate are slightly alkaline and have a pH near 8.4. Additions of

small amounts of strong acids or bases (alkalies) to solutions of sodium bicarbonate do not

produce the expected change in pH because the hydrogen ions (H+) or hydroxide ions (OH-)

are neutralized by the bicarbonate:

H+ + HCO3 H20 +C02

OH-+HCO3 H20+C032

Unlike acids and bases, solutions of sodium bicarbonate have a relatively constant pH over a

wide range of concentrations.

pH , Excess Basicity , & the CO2 System

Natural seawater is alkaline in nature due to its containing an excess of basic (+) over acidic

(-) ions. This 'excess basicity ' is attributable to bicarbonate (HCO3), carbonate (CO3), borate

(H2B03) carbon dioxide(C02) and carbonic acid (H2C03). All exist in equilibrium with each

other and with the hydrogen ions (H) present. It is a self-balancing system, and as such

natural variations are exceedingly small and rarely exceed the pH range of 8.O to 8.3. If one

of these variables is altered the complete system changes and a new state of equilibrium is

attained quite rapidly, This change is effected by several mechanisms related to these


(1) If the pH increases boric acid (H3B03) changes to H2B03+ H- , so releasing a hydrogen

ion to inter-react with the carbon dioxide system

(2) The carbon dioxide system (graphically illustrated below) *


.. . HCO3+ H . C03 + H

H 2C03

adjusts itself until a new state of equilibrium is reached. This also entails the inter-reaction of

atmospheric carbon dioxide though this takes place relatively slowly.

These mechanisms have been studied thoroughly and very accurate estimates are possible

for the reacting components.

The term pH is used as an expression of the hydrogen ion concentration, and as such this is

measurable easily and quite accurately. In natural waters this gives an accurate

representation of the 'status quo' but this is not the case with many synthetic

formulations especially those which omit boric acid or a boron salt, or those that increase

the quantity of sodium bicarbonate. In either of the above two cases the pH reading will

not give a representative indication of the condition of the carbon dioxide system, and the

speed of any equilibrium correction may be affected.


The hydrogen-ion concentration of aquarium and laboratory water is often measured using

colorimetric comparison methods. Dangers occur here : -

(1) See above paragraph relating pH to components used in any synthetic formulation.

(2) Normal Freshwater Colorimetric indicators are subject to ' salt error' and have to be

corrected for use in sea water, unless specifically designed for marine use

Fig. 6, pH Curves for Various pH-Influencing Substances

Consider a solution represented by point x on curve B. If hydrogen ions are now added to

the solution, what happens? The hydrogen ions react with the bicarbonate and are neutralized.

The bicarbonate concentration is decreased to point B, but we are in a region of the

curve where a change in bicarbonate concentration results in little change in pH.

Consequently, pH remains relatively unchanged in point y. From the curve, it is obvious that

pH will remain relatively constant over a range of bicarbonate concentrations. This is the

principle of buffering, or stabilization of pH.

Many chemicals can be used to prepare buffered solutions. In a marine aquarium,

bicarbonate is the principal ion responsible for stabilization of pH. Biological action produces

acidic substances that are subsequently neutralized. Continued addition of acid depletes the

buffer, which must eventually be replenished or a dangerous drop in pH may result [Point


The capacity of a system to neutralize additions of acid is represented by a property called

alkalinity. A solution with high alkalinity is relatively insensitive to moderate additions of


materials, whereas a solution with low alkalinity may experience a significant drop in pH

under similar circumstances.

Proper pH is essential because availability of hydrogen ions is important to many

biochemical reactions within living cells.

Buffers can help to maintain a proper pH in the aquarium

Small changes in pH can profoundly affect these reactions. Remember a change of one pH

unit means a tenfold change in hydrogen ion concentration.

The pH in a marine aquarium should be between 8.0 and 8.4, with 8.1 - 8.3 considered ideal. The pH

and alkalinity are maintained by buffers that are present in the initial salt solution, and, to some extent,

by carbonate gravel and coral. As buffer is depleted, it must be replenished. This is accomplished by

regular partial water changes, which-may be supplemented by careful addition of Sodium (bicarbonate

of soda) or Potassium bicarbonate.

Oxygen and

Carbon dioxide

Sufficient oxygen (O2) is essential to marine aquariums. A warm water marine aquarium

contains approximately 7 mg/l O2 at saturation, and the oxygen concentration should always

be maintained near saturation.

Fortunately, all that is necessary to accomplish this is vigorous aeration and circulation of the

aquarium water. Gas exchange takes place at the air-water interface. Oxygen dissolves into

the water to replenish that which has been used.

Animals (and plants in the dark) utilize oxygen to produce energy. In the process. carbon

dioxide (CO2) is produced, and released to the water.

Removal of carbon dioxide is as important as replacement of oxygen. If carbon dioxide

builds up in the aquarium water, it becomes more difficult for fish to release it from their

blood through the gills. Excessive carbon dioxide in the blood lowers its pH, which decreases

the capacity for carrying oxygen. In extreme cases, fish can suffocate even in the presence of

excess oxygen.

In seawater with a safe pH (above 8), carbon dioxide is converted to bicarbonate (HCO3-). At

lower pH values the proportion of free carbon dioxide increases. Some of this may be slowly

released to the atmosphere.

If aquariums are adequately aerated, and pH is properly maintained, there is little likelihood

of encountering problems due to oxygen depletion or carbon dioxide accumulation.



Marine animals produce ammonia as a metabolic waste. Additionally, ammonia may be

produced by bacterial action on uneaten food and other matter. The input of ammonia into

aquarium water is constant, and ammonia is toxic to marine animals.

Ammonia in solution exists in two chemical forms, unionized (NH3) and ionized (NH4+)

which considered together are referred to as total ammonia. Ionized ammonia is formed by

reaction of un-ionized ammonia with a hydrogen ion (H+): NH3 + H+ = NH4+

The proportion of ionized ammonia depends primarily on the availability of hydrogen ions,

and is a function of temperature, salinity, and pH.

The strong influence of pH is easily understood when one recalls that pH is actually a

measurement of the hydrogen ion concentration. In fact, because most aquariums operate

within a narrow range of temperature and salinity, the contribution of these factors is


Ammonia Equilibrium at Different pH Values at 220C.

pH 7.8 7.9 8.0 8.1 8.2 8.3 8.4 8.5%


97.7 97.1 96.4 95.5 94.4 93.1 91.4 89.5%


2.3 2,9 3.6 4.5 5.6 6.9 8.6 10.5

Equivalent amounts of total ammonia are more toxic at higher pH values. The Table shows

that at the pH values normally encountered in a marine aquarium (pH 8.0 - 8.4), a significant

proportion (4 - 10%) of the ammonia is un-ionized.

It has long been suggested that un-ionized ammonia is the toxic form, and that increased

toxicity at higher pH values is due to increased amounts of un-ionized ammonia. It is also

possible that ammonia is toxic in both forms, that higher pH values increase the toxicity of

both forms, and that the increase in unionized ammonia is coincidental.

So little is known about the exact mechanisms of ammonia toxicity that neither explanation

has yet been proven scientifically. It cannot be denied, however, that ammonia is toxic and its

presence in an aquarium is detrimental.

Fortunately, ammonia does not accumulate indefinitely. Certain bacteria obtain energy by

oxidizing it and, in so doing, convert it to a less toxic molecule, nitrite {NO2-)

Although less toxic than ammonia, nitrite is still dangerous. It affects the haemoglobin in the

blood, making it less capable of transporting oxygen. At worst, this can result in death. At

best, the animal is still subjected to stress from which it may or may not recover completely.

Results of recent research suggest that nitrite may not be nearly as toxic to some saltwater

animals as was previously suspected. Unfortunately, this has not been demonstrated conclusively

for the marine animals found in most aquariums and, until such time, any prolonged

exposure to nitrite ions should be regarded as unsafe.

Nitrite, however, like ammonia, is susceptible to bacterial action, which converts it to

relatively harmless nitrate ions (NO3-). The process by which ammonia is converted to

nitrite, and subsequently nitrate, is called nitrification.


The initial establishment of nitrifying bacteria is called conditioning. It is normally

approached by the early addition of one or two hardy animals to provide an ammonia

source, and then allowing sufficient time for bacteria to multiply.

In newly set-up aquariums, ammonia accumulates as a result of the continuous input of

animal wastes. Bacteria that utilize ammonia multiply and eventually the ammonia is

oxidized to nitrite as quickly as it is produced. As nitrite forms it, too, accumulates until the

bacteria that utilize it have multiplied sufficiently. Only nitrate continues to accumulate. The

Chart below shows a classic sequence.

During conditioning, ammonia increases, usually for a period of 1-2 weeks, ordinarily

reaching a maximum concentration of 3-6 mg/l NH3-N (Point A, Figure Below). The level

then decreases as populations of bacteria become established. After 3 to 4 weeks ammonia

should be virtually undetectable.

Nitrite appears shortly after ammonia. A maximum concentration is usually encountered in

2-4 weeks (Point B, Fig. 7), eventually decreasing to zero in 3-6 weeks (Point C, Figure

Below). This signals the completion of conditioning and the point at which additional animals can be

safely introduced.

Addition of more animals occasionally produces a modest increase in ammonia and nitrite, as bacteria

equilibrate to accommodate the increased load. These changes should be temporary and subside


The conditioning period may be considerably shortened or eliminated completely by

"seeding" a new aquarium with gravel from an older well established system. Using 10% of

conditioned gravel will permit much more rapid increases in population than would

otherwise be possible.


Phosphorous is encountered in the aquarium principally as dissolved phosphate (PO4--).

Animal wastes are the primary source. Phosphorous concentrations increase as the water

ages, but eventually level off. Maximum concentrations seldom exceed 3-6 mg/l (PO4-)3-P. No

direct toxicity problems have been associated with, phosphate, and its presence in small

quantities is of little concern but uncontrolled increases can result in algal blooms, followed

by their subsequent disastrous collapses.

Phosphorous is an essential nutrient for algae, and its absence will severely limit growth of

aquatic plants. An aquarium containing animals will always have phosphorous far in excess

of that required by the "casual" algae that may be present. However, there are occasions

when intensive culture of algae is desirable, perhaps for use as a food for other organisms. In

such cases, especially in the absence of animals, it is likely that phosphorous, as well as other

essential plant nutrients, will be depleted, and it will be necessary to maintain growth by use

of supplements.

Organic material

Presence of significant concentrations of organic matter is an important difference between

ocean water and aquarium water.

In an aquarium, animal wastes, excess food and excretions of plants result in accumulations

of organic materials that are never encountered in the ocean. These substances can have a

profound effect on aquarium life.

Non-living organic matter, either dissolved or particulate, is usually apparent upon visual


Dissolved Substances

High concentrations of dissolved organic compounds are identifiable by observation of two

situations. Either the water becomes highly coloured, or the surface foams excessively when

aerated. Frequently both occur simultaneously.

As aquarium water ages, it becomes increasingly yellow due to the presence of colored

organic molecules. The condition is unsightly, but is controlled, to some extent, by regular

partial water changes.

In some cases it is necessary to provide for additional means of removal. Activated carbon is

frequently used for this purpose. Activated carbon in an auxilliary filter will usually keep the

water sparkling clear, by adsorbing colored and other dissolved organic compounds.

Many organic compounds are surface active; they behave similarly to soap or detergents.

Surface active compounds result in a persistent foam on the surface of the water.

Surface active compounds are also conveniently removed by activated carbon, but an

alternate method utilizes the foaming phenomenon.

A foam fractionator, or protein skimmer is a device that is designed to maximize the amount

of foam produced, and continually remove it from the water surface. The foam forming

components are effectively removed from solution.

A third alternative is use of ozone to chemically "consume" large organic molecules. Ozone is

frequently used in conjunction with activated carbon or foam fractionators for maximum efficiency

and safety (activated carbon neutralizes excess ozone).

Removal of organic matter is necessary not only for the sake of appearance, but for the health

of the aquarium inhabitants as well. There is strong evidence to suggest that high organic

levels interfere with normal growth and development of fish, and may contribute to

increased susceptibility to disease. Also, bacteria utilize oxygen to consume biodegradable

organic compounds. This, in effect, increases the bio-load on the system, thereby reducing

the total stocking capacity of the system.

Particulate Matter (aka Detritus)

Particulate organic matter eventually accumulates in the filter bed/s as a fine, dust-like

material called detritus. It is formed from solid wastes and from dissolved organic molecules

that combine to form groups that are too large to remain in solution. Continued aggregation

results in the highly visible detritus within the filter bed.

Detritus is of little concern unless it becomes so substantial that the flow of water through

any filter bed is impeded. However, since its appearance is unsightly, it is usually removed.

The most common method of removal is physical; by gently "vacuuming" the gravel when

water is being removed for a partial water change. Various mechanical devices are also

available for cleaning the filter bed, and these may not require removal of the aquarium

water to be effective.

If detritus removal is conducted on a regular basis, there is little likelihood of encountering

problems associated with the cleaning. It should be noted, however, that the detritus has a

high surface area that is available for growth of nitrifying bacteria. In fact, some of the

nitrification capacity of the filter bed can be attributed to the bacteria upon the detritus


If allowed to accumulate for an appreciable time (several months), a significant portion of the

nitrifiers may be on the detritus. Its removal could result in a substantial decrease in

biological filtration capacity. In an aquarium that is loaded near capacity, this could be


An aquarium maintenance program should always include regular cleaning of the surface of

the filter bed.


Copper is given special attention because it is extensively used as a medication for protozoan

diseases of fish. Levels of copper, used for therapeutic purposes, are far in excess of those

normally encountered in nature.

Elevated copper levels may be dangerous to fish and invertebrates, but copper has a long

history of successful application when utilized properly. However, it is a heavy metal, and is

subject to the same instabilities discussed previously in the Trace Element Section. This

makes proper utilization difficult.

Copper treatment should be maintained within a safe, yet effective, therapeutic range (0.10-

0.20 mg/l) for at least 10 days. When copper sulphate is used, the copper concentration

decreases soon after addition to the aquarium water and the level must be maintained with

additional copper sulphate.

An accurate copper test kit is valuable, but most aquarists rely on the chance that regular

additions, according to manufacturer's recommendations, will be sufficient. When following

recommendations for regular additions, the copper concentrations. that result depends on

numerous conditions that vary in different aquariums. The actual concentration that results

may be useless, effective, toxic, or somewhere in between. Without an accurate analysis, it is

impossible to be certain.

For this reason, it is always preferable to utilize a separate aquarium for treatments. To

attempt treatment of a display tank with only one or two unhealthy specimens is flirting

with disaster.

During treatment, do not filter with activated carbon, charcoal or other adsorbents. They

remove copper quickly, and are, in fact, an excellent means of reducing the concentration in

an emergency.

Never use copper based medications if invertebrates are present, unless the formulation

specifically states that it is safe to do so.. Many are especially sensitive to it and may be


Recently developed medications contain copper that has been reacted with an organic

substance to produce compounds that are more stable in solution, and less toxic to fish. They

are also less toxic to parasites, and higher copper concentrations, which vary with different

products, are necessary to be effective. Their primary advantage is stability in solution. Once

an effective therapeutic level has been established, subsequent additions are unnecessary or

greatly reduced. Most are still conveniently removed by activated carbon or other


Water chemistry as a guide to

aquarium maintenance

Testing may be used to help indicate the quality of water in the aquarium. However, testing,

by itself, is neither beneficial nor detrimental to water quality, and is useless unless the

aquarist is aware of appropriate action, and prepared to take it, when tests indicate that it is


The situations discussed here are those most frequently encountered: new aquariums,

established aquariums, and hospital or medication tanks. A fourth situation, high density

rearing or hatchery aquariums, is a specialized subject which warrants its own literature.

Conditioning of new aquariums

(Yes, you may have read this paragraph a little earlier, but we feel it’s important enough to repeat……..)

In conditioning of new aquariums, a few hardy animals are introduced to provide a source of

ammonia. Simply setting up the aquarium and letting it operate for several days without animals

does absolutely nothing. Animals must be added to provide a source of ammonia for

the nitrifying bacteria.

Initially the system experiences elevated ammonia levels followed by elevated nitrite levels.

Both subside when sufficient populations of nitrifying bacteria are established.

Monitoring ammonia throughout the conditioning process is of questionable value. Little

can be done to prevent or compensate for the inevitable rise in ammonia. Even knowing

when the ammonia concentration falls to zero is unimportant. This is usually accompanied

by high nitrite levels, and it is still unsafe to increase the population of animals until the

nitrite concentration is zero, indicating the completion of the initial conditioning.

Nitrite appears shortly after adding animals to a new aquarium, and the maximum is usually

encountered in 2 - 4 weeks. The concentration should decrease to zero in 3 - 6 weeks.

Monitoring nitrite during conditioning provides a convenient measurement of progress

and will indicate the point at which additional animals can be safely introduced. An

approximate position on the nitrite curve can be estimated by comparing measurements on

consecutive days. Once the concentration begins to decrease, it is usually only a short time

before conditioning is complete.

In aquariums that have not been seeded with a substantial amount of conditioned gravel, nitrite

concentrations can exceed 5 mg/l NO2--N, and a test should be chosen that is capable of measuring the

high concentrations that are encountered during conditioning. Tests that have only low range

capability are not as useful because they indicate beyond their maximum readable concentration for

much of the conditioning period. Of course, it is essential that the test clearly indicate when the nitrite

concentration has fallen to zero.

Established Systems

Monitoring ammonia and nitrite in an established aquarium provides information on the

condition of the biological filter. Nitrification in the filter is so efficient that ammonia and

nitrite should be virtually undetectable.

Presence of ammonia or nitrite indicates that the filter is not capable of handling the

biological wastes to which it is subjected. Common causes include:

(1) Overcrowding.

(2) Overfeeding.

(3) Undiscovered dead animals.

(4) Medications.

(5) Insufficient circulation.

(6) Irregular cleaning of filter.

Overcrowding is frequently difficult to diagnose because there is no convenient method of

determining the carrying capacity of an aquarium. The maximum acceptable animal load

depends on a number of factors, including surface area and depth of the filter bed, particle

size of filtrant, and flow rate through the filter. Additionally, the type of animal will also affect

the amount that can be safely maintained.

There are numerous "rules of thumb" for the maximum allowable concentration of fish. One

author may suggest no more than 3 inches of fish per square foot of filter / surface area.

Another may indicate that 2 inches in length of fish per gallon is acceptable. There is much


On a purely subjective basis, it is safe to say that if an aquarium looks too crowded, it

probably is. Frequent fighting and general irritability of the fish are other possible


If elevated ammonia or nitrite levels persist, and you have ruled out the other possible

causes, then you may reasonably suspect overcrowding. Removal of some of the animals is

necessary to reestablish balance.

Overfeeding and undiscovered dead animals are similar situations. In both cases the

decomposing organic matter provides ammonia, which increases the load on the biological

filter. If the capacity of the filter is exceeded, elevated ammonia or nitrite levels will be


In either situation, the offending material must be removed, either by net or by vacuum

siphoning. The aquarium should then stabilize quickly.

Care should be taken when feeding to insure that significant amounts of food do not go

uneaten. The aquarium should be observed frequently to determine that all animals are alive

and healthy. Pay special attention to soft-bodied animals, such as anemones, which can

decompose rapidly, and foul the aquarium.

Medications may have adverse effects on the bacteria in the filter bed. If elevated ammonia

or nitrite levels arc observed shortly after medicating, then the biological filter has probably

been damaged.

If possible, the animals should be moved to another holding facility while a substantial water

change (50% or more) is conducted. Filtration with activated carbon may also help to remove

the medication. Under the best circumstances the bacteria recover quickly and the animals

may all be safely re-introduced. In some situations, it may be necessary to increase the

population slowly just as in a newly established aquarium.

Refrain from medicating in display aquariums. Such treatments are better performed in

"hospital tanks" that are reserved specifically for the purpose of medicating. Conditions of

treatment are easier to control and there is no risk to healthy specimens in the display tank.

For optimum performance, any biological filter must receive a constant, substantial flow of

oxygenated water. If circulation through the filter bed decreases appreciably, incomplete

nitrification can occur and ammonia or nitrite may be detected.

The situation is easily remedied by restoring normal circulation. The most common causes of

decreased circulation are:

(1) Plugged air stones or diffusers in airlift tubes.

(2) Damaged. blocked or “kinked” air lines.

(3) Worn out or weak air pumps.

(4) Worn out motors, impellors or other power filter components.

The problem should be corrected by repair or replacement of the defective item.

An appreciable portion of the filtration capacity of a 'biological filter may be due to bacteria

on the surface of detritus particles. If allowed to accumulate for some time, the removal of

this detritus results in an appreciable loss of nitrifying ability, and ammonia or nitrite are


If this occurs, it may be necessary to transfer some of the animals to a separate holding

facility-to allow the biological filter to re-equilibrate.

To prevent such occurrences, the filter bed should be cleaned regularly to remove

accumulating detritus by lightly vacuuming. Usually this is accomplished during removal of

water for regular partial water changes.

Aquarists frequently ask, "What is the maximum exposure level for ammonia and nitrite?" or

"How much can the fish tolerate without being seriously affected?"

Many studies have been conducted to determine tolerance levels for various species of fish.

Unfortunately, the studies are conducted on fish that are commercially valuable, such as salmon

and trout, and the results are not necessarily applicable to the types of fish in marine

aquariums. Precise information concerning tolerance limits of ornamental aquarium fish is

not available.

Nitrification in the filter should be so efficient that ammonia and nitrite should be

undetectable. The tolerance of the fish to ammonia or nitrite is irrelevant. Elevated levels of

ammonia or nitrite should alert the aquarist to a potential problem. If the condition exists for

more than a day or two, then the problem must be found and corrected.

Nitrate, the end product of nitrification, is the only form of inorganic nitrogen that is

detectable in a healthy aquarium. Its concentration increases continuously, unless limited by

regular partial water changes.

Since nitrate is relatively non-toxic, water changes are not conducted only for the sake of

limiting nitrate. There are additional benefits that, although less obvious, are perhaps more


Nitrate accumulation is accompanied by other changes. Buffers are depleted and pH

decreases. Dissolved organic materials increase. Phosphate increases. Concentrations of other

inorganic ions change. The environment becomes increasingly dissimilar to the natural

environment. This contributes the increased stress for the aquarium inhabitants, and

ultimately may result in disease or death.

It is in the best interest of the aquarist to control these changes as much as is reasonably

possible. We can never hope to duplicate the stability of the sea, but we can limit the inherent

instability and inefficiency of the aquarium with a conscientious aquarium maintenance

program. Nitrate testing can provide valuable information for this programme.

The rate of increase in the nitrate concentration is a function of the bio-load on the system.

Many other changes that occur also tend to be in proportion to the bio-load. Thus, nitrate is a

convenient "yardstick" to measure the relative biological age of the water. Maintaining

reasonable nitrate levels through periodic partial water changes also helps to control and

moderate other changes that are occurring in the water.

A maximum concentration of 20 mg/l NO3--N is recommended. However, in non-critical

situations, such as ornamental display aquariums, this level is frequently exceeded without

serious consequences. For these applications, maximum concentrations of 20 - 40 mg/l NO3--

N are probably acceptable.

Each month, 25% of the old aquarium water should be replaced with fresh salt water, and

this is usually sufficient to maintain nitrate at reasonable concentrations. Other activities,

such as breeding of fishes or feeding experiments, usually require more control and lower

concentration limits. In these situations, nitrate testing is indispensible because monthly

water changes may not be sufficient to maintain the desired water quality, and, in the

absence of any sophisticated equipment, nitrate level will be the most convenient indicator of

the condition of the aquarium water.

In addition to nitrate, the nitrification process also produces acid. This acid depletes buffers

and results in steadily decreasing pH, which, if uncorrected, will fall below ideal levels.

Monitoring pH allows the aquarist to make corrections before the situation becomes


Marine aquariums operate comfortably in a pH range of 8.0 to 8.4 with 8.1 to 8.3 considered

ideal. The aquarist should strive to maintain pH near the ideal, and to avoid wide


Occasionally the regular partial water changes are sufficient to restore depleted buffers and

control pH fluctuations. However, frequently it is necessary to add more buffer between

water changes in order to maintain the desired stability. Sodium bicarbonate is commonly


The sodium bicarbonate should be added when the pH approaches the low end of the safe

range. At this point, one teaspoon per 25 gallons should raise the pH approximately 0.1 pH


Always dissolve the sodium bicarbonate in a small amount of water before adding it to the

aquarium. Make changes gradually; no more than 0.1 pH unit per day. It is always better to

make small corrections frequently, rather than large corrections occasionally.

A common misconception holds that use of the proper gravel, such as dolomite or crushed

coral, is sufficient to prevent low pH. In fact, at the normal pH of a marine aquarium, the

effect of the gravel is slight. The effect of the gravel becomes significant only when the pH

falls below 8.0, beyond the recommended range. The gravel alone will not prevent significant

fluctuations in pH; some action on the part of the aquarist is always necessary.

Hospital and Quarantine tanks

A hospital tank is an auxiliary aquarium that is reserved for isolation and treatment of new

or sick fish. Typically, it is used for short periods and does not have a functional biological


Without a functional biological filter, ammonia is the first waste product that will

accumulate. Since a diseased fish is already in a weakened condition, the ammonia must be

controlled to prevent subjecting the fish to additional stress.

Ammonia can be controlled by partial water changes, and monitoring ammonia will indicate

when a change is necessary. Depending on the size of the tank and the size of the fish, frequent

water changes may be necessary to minimize ammonia toxicity problems. It may even

prove difficult to maintain less than 1.0 mg/l ammonia-nitrogen. The ammonia level should

be maintained as low as is reasonably possible.

Considering the inherent difficulties with hospital tanks, many aquarists question their

necessity. However, medication of established display aquariums should be avoided. The

effects on the system are often unpredictable. Additionally, should the aquarist encounter

unexplained problems in the future, he will always be uncertain whether residual

medications are a contributing factor.

A medication is a toxic substance. Although intended primarily to control parasites, few

medications are completely harmless to fish. Obviously, treatment of a disease can be

accomplished only with medications that are more toxic to the parasites than to the fish.

Some medications have a wide margin of safety. For others the effective therapeutic

concentration is only slightly less than the level that is toxic to fish. In any event, the animals

are subjected to a stress that may range from moderate to severe.

Additionally, some medications are harmful to the biological filter, and use in a display

aquarium can have serious, long-term consequences as discussed previously.

Healthy fish should not be subjected to the potential hazards of medications. A hospital tank

is the means of insuring safe treatment without risk to healthy fish.

All systems

Temperature and salinity should be monitored in all aquariums, whether they are new,

established, or hospital tanks.

Temperatures of 70 to 750F (21 to 240C) are ideal. Occasionally, during hot weather, it may be

impossible to maintain low temperatures.

At elevated temperatures, the oxygen dissolving capacity of water is less, while the

metabolism of the animals is speeded up, and they actually require more oxygen. In effect,

the holding capacity of the tank is decreased. In such situations, it may become necessary to

lower the population of animals in the aquarium.

Ideal salinities are 27 to 31 parts per thousand, which correspond to specific gravities of

approximately 1.020 to 1.023. Once the proper salinity is obtained, occasional replacement of

fresh water lost to evaporation will maintain the desired salinity with minimal fluctuations.

Water used for partial water changes should be adjusted to the salinity of the aquarium

before use. Water in hospital tanks should be adjusted to the salinity of the appropriate

display tank.

To increase salinity, add more salt. To decrease salinity, add more fresh water.

For both temperature and salinity, consistency is more important than absolute value. Temperature

should not fluctuate by more than 1 or 20F (10C) in a 24 hour period. During warm periods, adjust the

aquarium heater to a temperature only slightly below the maximum temperature to prevent excessive

cooling during the night. Salinity should not fluctuate more than 1.0 part per thousand (0.001 specific

gravity units) per week.

In Summation

Monitoring of various water chemistry parameters can provide valuable information to the

serious marine aquarist.

Routine monitoring of ammonia and nitrite may indicate a developing problem in an

established aquarium. Measurements of nitrate and pH helps develop a reasonable timetable

for routine maintenance, which is the aquarist's most valuable tool for continually providing

a healthy environment within the aquarium.

In newly set-up aquariums, nitrite measurements are an indicator of progress in the

conditioning sequence.

Temperature and salinity measurements are aids to maintaining a more stable environment.

Other measurements serve useful purposes in special circumstances, but are not routinely

employed by most aquarists. For example, phosphate levels may be of interest for intensive

algal culture.

In choosing test equipment always remember that the value of the test depends on its

accuracy. The accuracy of a test is a function of two factors, the accuracy of the standards and

the reliability of the reagents.

Standards, or comparators, are generally one of three types; colored liquids in sealed tubes,

colored plastic films or chips, and printed paper. Liquid and plastic types are usually more

reliable because paper types tend to discolor easily. Never store any standard in direct

sunlight or it will most certainly fade and become useless.

Reliability of reagents depends on the type of reagent and its stability upon storage. Any

reagents that have appreciably discolored should not be used. In general, liquid reagents are

more prone to deterioration than dry reagents. Refrigeration will extend the life of liquid


When in doubt, attempt to analyze a solution of a known concentration, to test for accuracy.

If such a solution is not available, at least attempt a duplicate analysis to test for repeatability.

Reasonable care and attention will benefit the aquarist who attempts to utilize the

information that can be gained through water analysis


ABSORBSION - The taking up of one substance by another, usually of a liquid by a solid,

involving weak chemical or physical forces. Water is absorbed by a sponge, but it is weakly

held, and may be easily removed by squeezing or drying.

ADSORBSION - The taking up of one substance by another involving strong chemical or

physical forces. Methylene blue, a chemical dye, can be adsorbed by activated carbon, and

then is extremely difficult to remove from the carbon.

AQUEOUS - Of or pertaining to water.

BIO-LOAD - The sum of the contributions and requirements ofall the living organisms in an


BUFFER CAPACITY - The ability of a solution to resist changes

in pH.

CHLORINITY - The weight, in grams, of the chloride ions (Cl-) present. This is often

expressed as parts per thousand

COMPLEX - A metal ion surrounded by an organic molecule to which it is tightly bound. The

organic molecule insulates the metal ion and reduces its activity in solution.

COMPOUND - A collection of atoms of two or more elements,connected by chemical bonds.

CONDITIONING - The process of establishing a biological filter in the aquarium. Sometimes

called run-in.

DENSITY - Weight per unit volume. For example, pounds per cubic foot.

DETRITUS - Loosely packed, insoluble solids that accumulate on the aquarium floor.

DISSOCIATON - The reversible breaking apart or separation of a molecule into two or more


ELECTRON - An elementary particle of an atom that carries a negative electrical charge.

ENZYME - A large molecule that promotes biochemical reactions.

EQUILIBRIUM - A state of balance between opposing forces.

Chemical equilibrium is a condition where two opposing

chemical reactions are occurring at the same rate.

HAEMOGLOBIN - An iron-containing pigment that is responsible for oxygen transfer in the

blood of many animals.

INORGANIC - Referring to chemical compounds that do not

contain carbon.

MILLIGRAMS PER LITER - A unit of concentration measurement in the metric system that

denotes weight per volume. A milligram is approximately 1/28,000 of an ounce

NEUTRON - An elementary particle of the atom that is not electrically charged.

NITRIFICATION - The sequence of oxidation, by bacteria, of ammonia to nitrite, and nitrite to


NITRIFIERS - Bacteria that are capable of oxidizing ammonia or nitrite.

ORGANIC - Referring to chemical compounds that contain the element carbon.

OSMOSIS Referring to flow or diffusion of substances through a semi-permeable membrane,

such as a cell wall.

OXIDATION - Chemical addition of oxygen to a substance,

often by a series of reactions. Oxidations may be vigorous

(fire) or mild (bacterial oxidation of ammonia).

OZONE - A highly reactive molecule composed of three atoms of oxygen. A molecule of

normal atmospheric oxygen is composed of two atoms of oxygen.

PARTS PER MILLION - A unit of concentration measurement that denotes weight per weight

in equivalent units. One part per million can mean one gram per million grams or one pound

per million pounds or any other unit of weight may be used.

PROTON - An elementary particle of the atom that carries a positive electrical charge.

PROTOZOA - Microscopic animals, many of which consist of

only a single cell.

SATURATION - State of being filled to the maximum extent.

SOLUTION - A mixture of two or more substances that is uniform throughout. A sample

taken from a solution will have the same composition and properties as every other sample

taken from the same solution - regardless of the size of the samples.

SURFACE ACTIVE - Capable of modifying the properties of a

liquid at a surface or interface.

Calypso Research Report. APPENDIX A .


To 90 kilograms of distilled or de-ionised water at 20 degreec C.add:-


Common Name Exact Chemical Formula and

Grade Weight (grams)

Purity %

Sodium chloride NaCl Analytical 99•96 2,378•0000000

Sodium sulphate Na2S04 10H20 Analytical 99•0 896•8100000

Magnesium chloride MgC12 6H20 Analytical 98•0 1,078•6500000

Potassium chloride KC1 Analytical 99.8 72•7500000

Sodium bicarbonate NaHCO3 Analytical 100•0 18•3697500

Potassium bromide KBr Analytical 99•5 9•7351110

Strontium chloride SrC12 6H20 Analytical 98•O 3•1455500

Boric Acid H3BO3 Analytical 99•5 2•5668000

Sodium fluoride NaF Analytical 99•0 •3000000

Lithium chloride LiC1.H20 Analytical 99•0 •1697709

Rubidium chloride RbCl Laboratory 90•0 •0276666

Potassium iodide KI Analytical 99•8 •0077333.

Aluminium potassium sulphate A1K(SO4)2 12H20 Analytical 99•5 •0044271

Manganese chloride MnCl2 4H20 Analytical 98•0 •0007655

Biotin •0000112

Cholic Acid •0000097

Vitamin B6 •0000095

Vitamin B12 •OD00075

Inositol •0000001

Pyridoxine •OD00001


To 4 kilograms of distilled or de-ionised water at 20 degrees C.add:-

Calcium chloride CaC126H20 Analytical 98•0 221•0165000

Sodium phosphate Na2HP04 12H20 Analytical 99•0 •0250000

Sodium silicate Na2Si03 5H20 Analytical 95•0 1•1313666

Sodium molybdate Na2Mo04 2H20 Laboratory 98•0 •0005750

Sodium selenate Na2Se04 10H20 Analytical 99•0 •0022750

Sodium metavandate NaVO3 Laboratory 98•0 •0005550

Uranyl acetate Uranyl acetate Analytical 99•0 •0002610


* Refer to the following notes

prior to adding this part.

To 100 grams of distilled water


3 mg. ZnS04 7H20

2 mg. Na2HP04 12H20

4 mg. Na2Mo04 2H20

0•6 mg. NaVO3

10 mg.FeCl3 6H20

3 mg.A1K(SO4)2 12H20

2 mg.Na2 HAs04 7H20

0.1 mg.CoCl 6H20

1•0 mg.BaCl2 2H20

1•0 mg.MnC12 4H20.

0•4 mg.CuS04 5H20.

1•0 microgram.K2Cr2O7

(All of the above should be of analytical or an equivalent grade of purity

Note: Initial precipitation will occur with both parts two and three. These will rapidly redissolve

when these parts are added to part one

Calypso Research Report. APPENDIX A continued

When all three parts of the formula are dissolved, part two should be added to part one, followed by part three being added to these two

when mixed.

The quantity of the solution called here part three can be adjusted according to final requirement:-

(1) If 'Open Oceanic' or 'Tropical Reef' water is desired add 50% of the part three stock solution.

(2) If Temperate Coastal water is required add all of part three.

(3) If an intensified culture medium is required the quantities of salts listed in part three may be doubled, & the following salts also

added:- (to the final solution)

Magnesium nitrate. Mg(NO3)2 6H2O O.25 grams

Potassium nitrite. KNO3 0.015 grams

Ammonium chloride. NH4Cl. 0.015 grams

Ferric citrate. C6H507Fe5H20 0.015 grams

The final solution should be vigorously aerated for a minimum of one hour prior to use. then corrected to 1.025 S.G. it will yield a

solution conforming to the requirements of the the text tables. It will also show the following characteristics:-

pH 8.2 +0.1

Salinity 35 0/oo S.

Chlorinity 19 0/oo Cl.



 Calypso Publications  Registered at London 2225933 1978  established in 1978 as the publishing arm of Calypso

Anyone wishing to follow on further information regarding the contents of this site is encouraged to visit  and   

Website design and production by Gerald Jennings.  Copyright   The Calypso Organization 2016