Medications

Hi Nico,
I'm not sure if this will actually answer your questions or lead to more...
I doubt anyone can tell you the percentage of 'good' bacteria (Nitrosomonas and Nitrobacter) that are destroyed by any given medication. I have heard that a well established bio filter will suffer a bit less than a filter that's just finished cycling. Many (most?) medications are harmful to the bio filter in some degree, even some that claim to be completely safe. How damaging depends on many things including the dosage, the amount of 'binders' in the tank (carbon, mulm, etc.), water chemistry and more.
I'm not sure I understood your second question correctly, but if you're asking what people use to remove medication residue, the best thing in my opinion is filtering through carbon. Many medications break down quickly in the water and a water change after the last dose of medication is finished would probably suffice, but using carbon for 48 hours will ensure that all traces of meds are removed.

It's hard to say exactly what effect a med will have on the biofilter without knowing which meds you're talking about.

While there is evidence that the nitrifying bacteria we want to keep are not the Nitrosomas and Nitrobacter that were identified (Nitrospira is more likely), you nevertheless have to be careful about dumping anything with antimicrobial properties into your tank.

Not all meds will equally affect every type of bacterium (that's why we have different classes of antibiotics, for example), the 'broad spectrum' antibiotics are more likely to cause problems.

Easiest, though, would be for you to post the med name or active ingredient and we could share our experiences with it.

HTH,
Jim

I just follow the instructions on the meds. Some caution against using on a particular fish. Paragon, for example, has a warning that it should not be used with certain kinds of fish.

Is it true that different medications have different effects on different types of fish i.e catfish to angels.

Some fish (like tetras) are weaker to large doses of medications and fish without protective scales (catfish, loaches) have real problems with them.

Nearly all meds are at least mildly toxic to fish (they work by being not quite toxic enough to kill fish, but enough to kill nasty disease causing organisms, plus snails, shrimp, and plants). Thus medication is can push very sick fish over the edge.

Just about any medicine used to kill parasites, bacteria, or fungus is probably going to hurt the bio filter. It's very important to be on top of water changes when medicating.