Fish diseases are either systemic or infectious. Systemic diseases are either iatrogenic (induced by an external condition) or congenital. Nothing can be done about a congenital condition. An iatrogenic condition can usually be reversed by removing the cause. A congenital disease can usually be recognized as some kind of deformity or behavior that affects only one fish, while an iatrogenic disease is more likely to affect many or all fish.

Infectious diseases pose a unique problem of diagnosis. Most are external and parasitic in nature. Parasitic infestations, however, are often accompanied or followed by secondary bacterial or fungal infections. Even the experts have problems identifying specific disease conditions. Internal infections are even more difficult to diagnose and treat. Internal infections should be treated with antibiotics added to food or with Focus™.

The best treatment for infectious diseases is prevention. New fish should be placed in quarantine and treated prophylactically before being added to a community tank. This is particularly true for a reef tank! If a sick fish is found in a community tank, then quarantine it for treatment. Treat both the known sick fish and the community tank. Treatment of healthy fiish in the community tank may be dispensed with if the infection is not particularly contagious. If a quarantine tank is unavailable then one must weigh the value of the fish versus the value of the whole tank while considering the inherent risks of whole tank treatment. If uncertain of the infectious agent, then treat with a broad spectrum agent of low cost (such as ParaGuard™ or PolyGuard™. If you know specifically what the disease agent is, then treat with the appropriate specific medication. Do not use antibiotics indiscriminately. Use non-antibiotic disinfectants first. If they fail, then turn to antibiotics. Frequent water changes and replenishment of medication are important.

Avoid the use of chemicalfiltration, ozone, and ultraviolet sterilizers during treatment. Any effective UV sterilizer will rapidly destroy almost any medication on the market. Do not treat a community tank unless the biological filter is strong and well established. Even medications that do not permanently damage the filter will retard it temporarily. Do not medicate while trying to establish a biological filter. Always be alert to the potential danger of ammonia or nitrite during treatment.