Water Chemistry

by James Montgomery

Why do I need this Information?

ost fish are fairly adaptable or we would not be able to to keep them. However there are certain species which are not so adaptable, especially when breeding them is concerned, also there is optimum water condition and quality for each species and while, by virtue of their adaptability, they may survive in other conditions, one will never see them in their best condition and displaying their full colourful beauty.

What is wrong with my tapwater ?
Nothing at all for the purpose for which it is intended. The various water authorities have a duty to produce water of a potable quality, this means that it is suitable for humans to use, without any additional treatments for the purpose of cooking and drinking. lt does not mean it is perfect for fishkeeping indeed as it is 'pure' and some of these chemicals remain in the water it follows that freshly drawn tapwater can in fact be harmful to your fish. A case in point involves a gas named Chlorine. This gas is used in the purifying process and a certain amount becomes dissolved in the water. Fortunately it is a volatile gas and will escape to the air if the water is drawn from the tap some 24 hours before use and allowed to stand in a container with the surface exposed to the air. An excess of Chlorine is quite capable of killing delicate tropical fish and is unpleasant to the human palate as you have probably discovered from time to time when drinking water freshly drawn. The hardness/softness and acidity/alkalinity of water from various localities differ considerably so the serious fishkeeper must make the effort, quite considerable at times to change the nature of the tap water to that suitable for his or her fish.

What does hardness/softness and acidity/alkalinity mean ?
These are terms used to describe certain qualities of the water concerned. A simple explanation is that hardness/softness relates to the amount of salt which the water has acquired since leaving the cloud, from which it originated, as rain. Hard water contains a lot of these salts while soft water contains little. Acidity/alkalinity of water refers to the ability to neutralise alkali/acid. It should not be confused with the acid/alkaline ph value shortly to be mentioned.

How do I know what sort of water I have got ?
Fortunately it is easy to check the quality of water by very simple tests. There are various 'test kits' on the market and although at first site they appear expensive, when one considers that only a few drops from them are required to carry out a test it follows that each package can complete several tests, thus making the cost per test reasonable. The normal procedure is to take a small measured quality of water and to add to this a specified number of drops from one or more solutions in the test kit and then compare the resultant colour of the water to the colour chart.

How do I measure hardness/softness ?
This can be measured in various ways but generally accepted method relating to fishkeeping is to use the German method of degrees, the higher number of degrees the harder the water. The question of hardness is complicated by the fact that the three types of hardness are generally considered total hardness, carbonate or temporary hardness and non-carbonate or permanent hardness.

What is Total Hardness ?
Total hardness is self explanatory and refers to the total amount of salts which are contained in the sample of water. The salts which are of interest to us are bicarbonates, carbonates, and sulphate's of calcium and magnesium.

What is Carbonate or Temporary hardness ?
This is is a little confusing in that it refers to the bicarbonates and small amounts of carbonates (carbonates are not very soluble in water). This type of hardness may be removed by boiling water which converts the bicarbonate into virtual insoluble carbonate which is precipitated. This is the explanation for 'fur' found in kettles in hard water areas. For those with soft knowledge of chemical symbols what happens is as follows, CA (HCCO 3 ) 2 = (When boiled) Ca CO 3 + CO 2+ H2O. Calcium bicarbonate*, Calcium carbonate, Carbon dioxide, Water (*Bicarbonate is know scientifically known as Hydrogen carbonate) in other words the Calcium bicarbonate is broken down into calcium carbonate (mostly deposited on the inside of kettles or other vessel used), Carbon dioxide (a gas which escapes into the air) Water.

What is Non carbonate or permanant hardness ?
This is found by subtracting the carbonate hardness from the total hardness and is caused by the amount of calcium and magnesium present in the water, normally in the form of sulphate's, nitrates and chlorides. This type of hardness can not be remove by boiling as in the case of carbonate hardness. There are two main methods of removing this type of hardness, first by boiling away the water in a closed vessel the steam being conducted to a condenser where it is cooled, usually by a water jacket and thus condensed back in to water which is soft having left the salts behind. This method is expensive in operation but does produce virtually pure water, in fact this water is so pure that it would not support fish life as certain 'trace elements' which they need have been removed. The second method is by ion exchange,as used to produce distilled water for car batteries. This method uses an ion exchange resin, often sodium zeolite,which will exchange its sodium for the calcium in the water. The terms used in respect of hardness using the German system are :- 0 GH= General hardness (permanent) :- 0 KH= Carbonate hardness (temporary).

What are the the other methods of reducing water hardness ?
Go to our article section for more information on reducing water hardness.

What is pH. ?
The pH value indicates whether a liquid reacts in an acidic, neutral or basic (alkaline) manner. The pH scale ranges from 0 (very acidic) to 14 (very basic), with neutral at about 7. The pH value shows the concentration of certain ions which are responsible for an alkaline or acidic reaction. Most freshwater fish and plants can only survive in the pH range of 6-8. Some specialist species require ranges of 5 or 9. Maintaining a pH level of around 7, in the neutral area is recommended for the following reasons.

As a one point fluctuation in the pH value corresponds to a tenfold alteration in the ions responsible for the change, any change in the pH value is stressful for all the organisms in the water, whether fish, plants or micro-organisms. Sudden deviations in pH levels may lead to increased susceptibility to disease in fish, poor growth in plants and may even kill micro-organisms.

Reference: JBL Biotope aquarium water. JBL. GmbH & Co.KG, D-67141 Neuhofen/Plaiz, Germany. 33p.


This article first appeared in the Greenock & District Aquarist Society newsletter "The Angelfish" October 1995. no 4. and is also duplicated on the Help index on Water Chemistry


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