I think you should read the label on the meds you are using and research each of the ingredients and what types of fish they can safely be used for.
Some fish are sensitive to certain types of chemicals and it can stress them out to the point where they have no defense against the disease or parasite they are being treated for. They die, usually needlessly.
I recently looked up Maracide, commonly used by a lot of people for pretty much everything. Maracide contains aniline green, which is malachite green. Malachite green is toxic to catfish, loaches and tetras. It's also not safe for dwarf cichlids, gouramis, livebearers and barbs. Maracide doesn't have those warnings on their bottles, but it's on the Malachite Green bottle. Perhaps there is very little malachite green in there and they feel they don't have to mention it. Perhaps they listed it as aniline green so that people won't realize it's malachite green. Dunno.
IMHO nothing should go in the water unless you fully understand what the reactions that medication will cause in each type of fish in your tank.
Roan