Most pet stores sell a variety of medicine, some for single diseases and some for multiple diseases.
Pet store bought medicine works nicely. Just look at the packages, they always have a list of what diseases they treat. If you would like to print out the entire list of fish ailments listed below, click here. To help make it easier to diagnose, I now have a quick diagnostic grid to help diagnose the more common ailments. Tiny white or green worms are attached to body or fin of fish, most likely on an open wound.