Understanding Water Quality
(Information Courtesy of Tetra Information Centre)

Creating the correct aquatic environment We know that different aquarium fish have different preferences with regard to water quality. Of course, it would not be possible to sell ready made 'guppy' or 'neon tetra' water for obvious reasons. However, any aquarist can reproduce the desired water of his or her fish by using some of the many aquatic aids now available.

Adjusting the water quality In the following information, the methods for altering the water quality are provided. With toxic pollutants such as ammonia and nitrite it is important to remove the toxins as quickly as possible. However, with hardness and pH (as with temperature) a sudden change can cause more problems than leaving the fish in unsuitable water conditions. Hardness and pH should therefore be altered slowly over a period of several days in order to avoid stressing your fish and making them susceptible to disease.

Water hardness Water hardness is a measure of the quantity of dissolved salts that are present. Pure rainwater has very few dissolved salts and is termed "soft water". As it seeps through the rocks and soil the rain water becomes enriched with various salts. This is greatly facilitated by the slightly acid pH of rain water. If the rocks are chalk or limestone more salts are dissolved than if they are sandstone or granite. Consequently, water from limestone areas is rich in dissolved salts and is hard, whereas water from sandstone or granite areas is low in dissolved salts and is soft.

Measurement of water hardness Different countries use different units and this can be confusing. The two most commonly used units are the German degrees of hardness ( 1° dH is equivalent to 10mg of lime per litre of water) and American degrees of hardness ( parts per million (ppm) of calcium carbonate). To convert from °dH into ppm calcium carbonate, multiply by 17.9.

General hardness The general hardness of water is a measure of the amount of calcium and magnesium salts that are present, with hard water containing more than soft water. The general hardness directly influences the internal functions of fish, plants and other organisms. The gill membranes and the skin of fish appear to be particularly sensitive to extreme hardness values. Affected fish may become slightly swollen and will rub against underwater objects  or "shimmy" in the water (showing a swimming motion without moving forwards or backwards). A suitable level for most tropical fish lies between 3° and 10° dH.

What to do if GH is too high Dilute the hardwater with clean rain water or distilled water. Use water softening resins, provided they are safe for aquarium use. Ensure gravel is lime free, as limestone gravels will increase water hardness.

What to do if GH is too low Add limestone pieces, cockle shell or coral sand into the filter or aquarium, until the required level is obtained. Marine salts can be used where a high GH is required for brackish water or marine fish.

Carbonate hardness KH (temporary hardness) As well as calcium and magnesium, most natural waters also contain bicarbonates as part of the total salt mix. It is these bicarbonates that make up the carbonate hardness or KH value. The bicarbonates have an important function in the overall chemistry of aquarium water. They act as a pH buffer preventing sudden changes in the pH value. Where bicarbonates are deficient ( i.e. low KH value), large fluctuations in the pH can occur under certain circumstances and the addition of a small amount of acid or alkaline water will cause a drastic change in the pH of the aquarium water. The higher the KH the better the pH buffering, but a very high KH can lead to a markedly alkaline pH. Carbonate hardness is also known as temporary hardness because bicarbonates change to carbonates and come out of solution when the water is boiled. Recommended values of the KH for stable conditions are around 2° to 8° dH, although certain fish do have other requirements.

What to do if the KH is too low Make up a strong solution of sodium bicarbonate and add it to the water a little at a time, until the desired KH is reached. Ensure water is well aerated during this process. Do not add the sodium bicarbonate solution directly into a tank containing fish or plants, as the sudden change may adversely affect the fish and plants. The adjustment should be made to water outside of the tank, and the adjusted water then added slowly to the aquarium. This should be carried out slowly over a period of several days, closely monitoring the pH during the adjustment.

What to do if the KH is too high Dilute the hardwater with clean rain water, distilled water, previously boiled water, or water treated with a commercially available softener. If practical, the tank can be filled with boiled water that has been cooled and aerated

Acidity, alkalinity and PH The degree of acidity or alkalinity of water is expressed in terms of the pH, which ranges from 1 (acidic) through 7 (neutral) to 14 (alkaline). The pH value is calculated from the total acid and base substances found in solution in the water. At a pH of 7 the acid substances cancel out the base substances, hence the water is termed 'neutral'. Bicarbonates in the water are important as they are able to bind with excess acids or bases and so prevent major pH fluctuations. A pH of 6.5 to 7 is suitable for most tropical fish species, but there are some exceptions.

What to do if the PH is too high The pH of the water may be reduced by adding peat to the aquarium or filter. Approximately 2 handfuls of peat, placed loosely in a fine mesh bag, should be added to every 2-3 gallons of water for several days before adding the water to the aquarium. Commercial pH adjusters are also available, but great care must be taken not to alter the pH too rapidly, as it could prove fatal to the fish.

What to do if the PH is too low Water may be made more alkaline (increase the pH) by adding limestone, coral sand or sodium bicarbonate to the water. This will also increase the water hardness, but most species that prefer alkaline water also require hard water.

Whichever method you choose Any pH changes must be conducted slowly, over a period of several days to avoid stressing the fish. Always change the pH outside of the aquarium except when material is added to the filter) to avoid any sudden fluctuations.

Nitrogen cycle Within the aquarium, fish waste together with any uneaten food and dead plants is decomposed in a process known as the nitrogen cycle. The nitrogen cycle involves the breakdown of fish waste, uneaten food etc. into ammonia or ammonium, ammonia or ammonium into nitrites, and finally nitrites into nitrates. Each of these stages is accomplished by means of bacteria in the presence of oxygen.

Amonia and amonium The first stage in the decomposition of fish waste and uneaten food is the formation of toxic ammonia and the relatively non-toxic ammonium. Both are easily converted into the other with the ratio of ammonia to ammonium being largely dependent upon pH. At a high pH (above 8.5) - mostly ammonia (toxic) At a low pH (below 7.5) - mostly ammonium (non-toxic) At levels as low as 0.25mg ammonia per litre of water, ammonia can be lethal to the fish, therefore regular tests should be undertaken in order to prevent it reaching toxic levels. In an established aquarium the ammonia concentration should be very close to 0mg per litre . If it is not it suggests that: a. The filter or tank has been recently set up and has not matured. b. The aquarium is overstocked. c. The fish are being overfed. d. The filter is not functioning correctly. e. There is excess organic debris somewhere in the aquarium.

What to do if the amonia content is too high Immediately change one third of the water in order to remove some of the toxic ammonia. At the same time remove as much debris as possible from the aquarium and gravel. Increase aeration if possible and investigate the cause of the problem. Commercial products, such as activated charcoal and zeolite are available which can be added to the filter and which effectively remove ammonia. Methods of maintaining a low ammonia level are dealt with in the section on nitrites.

Nitrates Nitrite, the second stage in the nitrogen breakdown process is also poisonous to the fish. For this reason it too should be regularly measured in order to keep it under control. As far as possible the nitrite concentration should not exceed 0.2mg per litre of water. At a level of 0.5mg per litre the fish will be adversely affected. Raised nitrite levels are often an indication that the nitrogen breakdown system has been disturbed. They are usually preceded by increased ammonia or ammonium levels and the causes are the same.

What to do if the nitrate content is too high As with ammonia, immediately remove one third of the water, together with any debris from the aquarium and gravel. Replace it with conditioned tapwater of the same temperature, and investigate the cause of the raised nitrite level. Nitrite levels may be kept low by the following means: 1. Carry out regular partial water changes (20-30% of the water every 2-3 weeks) removing any debris that may have accumulated in the aquarium or gravel. 2. Increase the biological filtration. 3. Undergravel filters should be cleaned by using a gravel cleaner to remove debris from the gravel, and thus preventing it from becoming blocked. Occasionally the syphon tube should be placed down the uplift tubes of the filter to remove debris that has accumulated under the filter plates. The filter media from box filters and power filters should be rinsed in old aquarium water to remove excess debris. Do not rinse under the tap as the chlorine will kill the helpful bacteria. Clean the filters at each water change. 4. Maintain a sensible stocking level and feeding rate. The fish should generally be fed once or twice a day on as much as they will consume within 1-2 minutes. The recommended maximum stocking rates for various aquaria are as follows : Tropical freshwater aquarium - 1 inch (2.4cm) of fish length excluding tails for every 12 square inches (72cm²) of water surface area. Coldwater Aquaria - 1 inch (2.4cm) of fish length excluding tails for every 24 square inches (140cm²) of water surface area.

Where does nitrate come from Nitrate is the final product of nitrogen decomposition and, in comparison to nitrite and ammonia is considerably less harmful to the fish. Nitrate accumulates in the water and will be used up by the plants and algae to a certain extent. Consequently, it promotes plant growth, but in excess quantities it can also lead to an undesirable growth of algae. In almost all situations the nitrate is not absorbed completely by the plants. And in time, will accumulate in the water. Raised nitrate levels can be controlled by regular water changes, by the use of chemical filter media, or by encouraging dense healthy plant growth and shifting the ratio of fish to plants more in favour of the plants.

Nitrate levels Below 12.5 mg nitrate : clean water : very good for fish and plants 12.5 - 25 mg nitrate : water still quite good : good for fish and plants 25 - 50 mg nitrate : partial water change advisable : still satisfactory for plants 50 - 100 mg nitrate : change of water necessary : stagnation of plant growth. Growth of blue/green algae commences. Above 100 mg nitrate : water extremely polluted and no longer  wholesome for plants. Dangerous to fish. : In absence of oxygen, nitrate can easily turn into toxic nitrite. At these levels of nitrate, tests for nitrite should also be carried out regularly.