Diseased fish should be isolated whenever possible so they are not likely to spread infections among other healthy fish in the tank. The best way to isolate sick fish is to set up a hospital tank.

Hospital Tank

The hospital tank should have no substrate or live plants. Provide shelter with over-turned flower pots and use plastic plants to help comfort the fish. Use a sponge filter or internal box filter that does not use chemical filtration or Carbon, for these products will remove many types of medications. It is not recommended to use a strong power filter as the water disturbance may aggravate ailing fish. The tank should be furnished with a reliable heater that will not permit much temperature variance. To protect fish from heater burns, the heater should be enclosed in plastic mesh or other other means of coverage. The tank should be dimly lit and kept in a dark room (Some pathogens do poorly in absence of light). Lastly, the tank should be furnished with an air stone to provide oxygen as some medications reduce the amount of free oxygen in the water.

When adding the fish to the hospital tank, try to have the water conditions as close to those from where the fish is coming. The initial stress is reduced when conditions are similar. After treating the sick fish, disinfect the tank with dilute hydrochloric acid or potassium permanganate. Let the chemical stand in the water for two or three days and then thoroughly clean the tank. After disinfection, the biological filtration should be restored, so the tank will be ready for the next sick fish.

The hospital tank can double as a quarantine tank. Ideally, all new fish should be quarantined for three to six weeks before they are added to the main tank.


An alternative means of treating a fish is to give it a short "bath" in a bucket containing water and a medication or salt. Chemicals for such baths, such as Formalin, can be found in aquarium stores. A salt bath can be used for a wide range of disorders. The length and concentration of the bath can be varied

Heat Therapy

Heat therapy of raising the water temperature, can be administered to kill certain parasites. Heat therapy should only be used in clean tanks with an abundant supply of oxygen. The temperature should be raised gradually by 1.8�F (1�C) an hour until the desired temperature is reached. During this time, the fish's condition must be monitored, because sometimes stressed fish cannot handle such a temperature change. Discontinue treatment if any side effects occur.

Medicated Foods

One means of combating internal parasites is to use a medicated fish food.

Warning about Commercial Medications

Commercial fish medications are not regulated by any government agency. This means that some commercial medications have not been tested for safety or effectiveness. Thus some medications are completely useless and may be even harmful to aquarium inhabitants. It is suggested that the hobbyist only purchase medication with the ingredients, and their concentrations, printed on the label. A list of ingredients only is as good as the aquariasts knowledge of the ingredients' effectiveness, so look for compounds listed in this, and other books. Well-known brands (i.e. Tetra) are usually safe bets, but one can never be sure unless the ingredients are available.

Killing a fish

Sometimes killing a fish suffering from an incurable disease is more humane than allowing it to continue suffering. There are several acceptable ways to kill a fish: severing the spinal cord just below the head with a sharp pair of scissors; placing the fish in water and rapidly cooling the container with ice; or overdoing with an anesthetic (Alka-Seltzer�).

Being Prepared for Disease

It is always a good idea to be prepared for an outbreak of disease. Thus one should keep all the supplies, not necessarily a number of medications, that they would need for disease treatment. Among the materials that should be kept are a hospital tank, buckets, and salt. The aquariast should also have knowledge of their fish's normal behavior � when they feed, how they swim, what they look like, when their active � so that they can know when the normal behavior has changed.

Procedure to Treat Ailing Fish

If a fish is ailing, there are several steps that should be taken prior to using medication.

1) Take a look at the ailing specimen, and take note of what is different from normal.

2) Check to make sure that all environmental conditions are in order, because the number one cause of stress, ailing behavior, disease, and death in aquaria are environmental problems. Test the pH, ammonia, nitrite, and nitrate levels, and if possible, the oxygen content. If these are in order, make sure that no other toxins such as paint fumes, pesticides, or cleaning agents could have entered the tank. If the answer is no again, make sure all accessories are operating properly (heater, air pumps, filter, etc.). Try to see if another tank mate may have been on the aggressive. Run down the list of the fish's requirements to see that they are all in order. Remember that tank layout and dietary deficiencies also can affect the fish's health.

If you find that one these conditions is off, then take steps to fix it. If the water chemistry is the problem, make water changes until the problem is fixed. If everything checks out, it is time to move on to the next step.

3) See that the hospital tank is in order, and set up two buckets full of water (The water should match the main aquarium's water conditions and be dechlorinated.). The buckets should be at least 2.5 gallons (9.5 L), though 10 gallon (38 L) tanks are preferable for large fish. Be sure that the containers are well-aerated.

4) Move the ailing fish by net to the first bucket. Add 3/8 TSP of salt per gallon (0.5 g/L) every two minutes for 10 minutes. Using the net, move the fish to the next bucket of fresh water for 30-45 minutes. After 15-20 minutes, add 3/8 TSP of salt per gallon (0.5 g/L) again.

5). Net the fish and move it into the hospital tank. Be sure to change the water daily (30-50%). After a day, move the fish into a shallow, clear bowl. Examine the fish for parasites and evidence of disease. If necessary, use a magnifying glass.

Treat the water accordingly.

6) Keep the fish isolated for at least 10 days.

Specific Diseases that Affect Tropical Freshwater Fish