Preventing fish disease

Water quality

The single most important factor in fish health is water quality. Dirty water-water that has free floating particulates and decaying organic matter- is low in oxygen, can interfere with fish respiration, and is a haven for pathogens and parasites. Proper mechanical and biological filtration promote a healthy system along with regular water changes.


Fish under stress are very susceptible to disease. Stress is caused by poor water conditions, sudden fluctuations in temperature- water parameters and other environmental conditions, poor diet, fear from aggressive fish, and any ongoing irritation such as to the skin or gills. Under constant stress the fishes immune system is lowered. The solution is the obvious: keep the water clean, well oxygenated, and stable and keep fish that are compatible with each other.


Disease is often introduced when adding new fish or animals to the community. To prevent this it is a good idea to have a small quarantine tank up and running ahead of time ready to put the new arrivals in and keep them there for two or three weeks to look for signs of disease before adding them to the community tank. If signs of a disease appear during that time, you treat the diseased fish before adding them to the community tank. This hospital tank should already be up and going with a viable biological filter long before adding the new fish. Otherwise adding fish to a tank that has not yet been cycled and is in itself unstable will cause the fish great stress and put them at risk even if they carry no disease. A five to ten gallon aquarium is usually sufficient unless you are talking about a very large fish. My hospital tank is a simple ten gallon, bare bottom with a small sponge filter. I have a couple guppies in it just to keep the tank cycled and ready for any new arrivals. The sponge filter is inexpensive, easy to clean, and very effective as a biological filter.

Other outside introduction

If you are transporting an infected fish from one tank to another in a net, the net should be disinfected before it is used again. Hydrogen peroxide or bleach works well. Just be sure to rinse thoroughly in clear water to remove any residue. Live plants may also be a carrier and can be treated in a disinfectant dip such as alum or potassium permanganate which is a very strong oxidizing chemical. One teaspoon in a two gallon bucket of water is all you need. Simply soak the plants in the solution for 15 or 20 minutes and then add the plants to your aquarium. Leftover residue on the plants is not harmful to the aquarium inhabitants. In fact in trace amounts it is used to treat fish infections, but in any larger amount it may kill fish and plants as well as the bacteria in your filter, so you should never add this chemical directly to the aquarium.