Before you use any medication on your tank be sure to properly diagnose the fish disease and try to figure out why your tropical fish have the disease. Many diseases are brought on by the tropical fish being stressed due to transport or water quality issues. If you've just set up your tank, please read about new tank syndrome. It's a very good idea to have a small quarantine tank for new fish so that you may monitor the fish for a few weeks before adding the fish to your main tank. You can also use the quarantine tank for your fish that come down with a disease and can avoid adding chemicals to your main tank. Always practice good fish acclimation techniques and don't rush things. Try to determine the underlying problem before medicating. Often times there are water quality issues that need to be remedied first. Get and use an aquarium test kit and take the appropriate measures to correct the water in your aquarium. Whenever you use any type of medication on your tropical fish, first remove any carbon in your filtration system. If left in, the carbon will remove the medication from the water, doing you no good. Read the directions on the medication bottle very carefully! To sum up, first determine the cause of the freshwater fish disease, fix any obvious problem(s) (water quality problems and/or tank mates), figure out which disease your fish has by closely observing the symptoms and then treat if necessary.

Eggs and Fry Diseases and disorders of eggs and fry	Essential Skills Essential skills to looking after your koi and pond fish
Koi Diseases and Other A list of common Koi and regular fish diseases and infections	Prevention of Disease Preventing possible disease in the fish caused by various avoidable factors
Treatments Medicines and treatments to common diseases and infections