Disease Prevention

In fish as in humans it is often far easier to prevent a disease from developing than to treat an advanced illness. The most important factors contributing to disease are:

Crowding
This is not an actual cause of disease but contributes to the rapid spread of any infection. This occurs because of a number of effects, including a shortage of oxygen dissolved in the water, excess waste products, generally weakened fish, and the obvious fact that the fish are closer together in a compact area and infectious organisms have a short and easy path from one fish to the other. The hobbyist should realize how abnormal an aquarium environment is to a fish whose natural surrounding are a lake, river or stream.

Overfeeding
This contributes to disease not so much from having the fish actually gorge themselves, but because uneaten food on the bottom of the tank will rot and pollute the water. In a tank with coarse gravel the fine food particles gradually drift into the deeper layers of gravel and may also contribute to rotting the plant roots. Occasionally fish will actually overeat and may show obvious distress. This is most likely to happen if very coarse particles of dried food are fed which may swell after they are eaten and actually obstruct the fish.

Inadequate Diet
Fishes maintained only on poor quality dried foods such as wafer foods will be stunted, weakened and subject to a variety of infections.

Water Changes
Approximately ten to twenty percent of the water in a tank should be changed weekly under ideal conditions. This prevents the build-up of excess nitrogenous wastes and will help keep the entire tank in good condition. In hard water areas this routine will also prevent the build-up of excessive hardness. Rapid changes in temperature, pH, or hardness will have a weakening effect on fish. Most fish will do well at a pH of about 7 and can survive in a range from 6 to 8. A rapid change from 6 to 8, however, will bring on immediate signs of distress. Tropical aquarium fishes do well at a temperature of about 75°F and can tolerate temperatures from 65 to 90°F or higher if the changes are made gradually. Fishes in a large body of water can tolerate a surprisingly low temperature, probably because of the longer period of time the water takes to cool.

Small quantities of water can be added to any tank directly from the tap if the temperature is approximately that of the aquarium, without any de-chlorination or aging necessary. If all of the water is to be changed or if a new aquarium is to be set up the water should be aged overnight before the fish are added. This allows the chlorine in the tap water to dissipate of its own accord and also allows excess air dissolved in the water to decrease. This process can be sped up by using commercial anti chlorine compounds available in aquarium shops, using recommended amounts. In some parts of the country tap water may be used without aging but the hobbyist should experiment with his local water before trying this with valuable fish.

New Additions
Most hobbyist have had the unfortunate experience of introducing new fish, plants, snails, or accessories into an established tank and noticing the sudden onslaught of disease. Ideally, new fish should be quarantined for a week or two in a separate tank while waiting for the possible development of signs of any infection the fish may be carrying. Once precaution is to treat the fish for parasites even though none are apparent. This may be done by using a formalin dip. Some hobbyists also routinely treat their quarantine tank with acriflavine or malachite green. The new plants may be decontaminated using commercial products available from aquarium supply stores. The question of snails, clams, and mussels is an open one. These animals can serve as hosts for a variety of parasites, some of which may affect aquarium fish.

Great care should be taken with materials which were not specifically intended for aquarium use such as homemade spawning mops, old porcelain ornaments, or rocks of unknown condition picked up in the field. If such items are to be used, it is safest to test them in a separate tank with inexpensive fish.

Contamination
The careful hobbyist will reserve a special net for any tank containing diseased fish, and will either sterilized it before using it on healthy fish, or destroy it. The aquarist's hands should always be washed after handling a diseased tank.

Poisoning
Fish are very susceptible to poisoning by many insecticides which may be used around the house. These should be avoided altogether in the fish room if possible, especially if they are in the form of sprays. Fresh paint may also be a source of toxic vapor for a period of hours after application. The safest course, if a nearby room is to be painted, is to cover the tank with several payers of paper and seal it with tape round the edges. Some of teh newer paints dry rapidly and are less likely to create problems.

Cleanliness and Filtration
There are two ways of setting up a large aquarium. The most natural situation is to have a large unfiltered tank which is well planted and contains only a few fish. This should require no aeration. Over the course of time a thick layer of mulm builds up on the bottom. This is combination of fish waste and fragments of deteriorating plant leaves. A tank of this type has a natural appearance and should be left alone without frequent changes of the fish population. The number of fish that can be kept in this way is limited.

Most hobbyists prefer a filtered tank with a larger potential fish population and a clean bottom free of mulm. Both outside and bottom filters are equally effective in removing particulate material from the water. Bottom filters have the additional feature of supplying effective aeration as well as filtration. Subsand filters work on a different principle and draw the fine particulate matter down into the gravel where an aerobic (oxygen-loving) bacterial culture builds up and breaks down the filtered material into harmless compounds. This type of filtration is usually effective and will keep a tank crystal clear in most cases but it is not too effective in the case of large, particularly dirty fish like goldfish. The subsand filter also seems to have an inhibiting effect on plant growth. A bad feature about this filter is that once the filter is established it cannot safely be turned off. The aerobic bacteria will diet and anaerobic bacteria which can live in the gravel without the constant flow of fresh oxygenated water will rapidly take over and may putrify the water.

A similar effect can occur if antibiotics are used in a tank with a functioning subsand filter. In this case the aerobic bacteria may be killed by the antibiotic and subsequent cloudiness can occur. A thick layer of gravel must be used with a subsand filter to make the filter effective. Other tanks need a layer of gravel only think enough to adequately root their plants. An even thinner layer of gravel can be used if the aquarium plants are grown in individual pots. This practice has an additional advantage in enabling the hobbyist to move the plants for cleaning the tank or for netting fish.