Some bacterial infections in fish show up like fuzz too. People fuzz is usually fungal, fish are a little different. A UV in the system might help, antibiotics might help, but identifying the type of bacteria and targeting it works best. Most shops don't do that. They look at symptoms and throw something broad spectrum at it. Its obviously not anaerobic, since its living on the surface of the fish. I forget which antibiotics you can get for fish, I have been working on people too long. Kanamycin does mostly gram negative some gram positive. Penicillin based does mostly gram positive. Metronidazole does anaerobic (internal) infections and parasites. So, if you were in Denver I'd say hit me up and we can gram stain the bug and target it. But without that you have a few options. If you can get your hands on an agar bacteria plate, catch the fish take a q-tip swab the infection and spread it all over the plate. Put a tiny bit of the drugs you want to know if will be effective in small spots. Label them. Let it grow on a counter at room temp overnight. Which ever drug spot doesn't look covered in nasty bacteria worked. I taught this trick to the local fish store. They loved it. But you have to get your hands on agar for it to work. I used to mix kanamycin and metronidazole into the food and feed that to my shrimp when they got sick, between the two it killed pretty much anything, except my shrimp. A UV can be huge though. It will kill the bacteria that are free floating in the water (and algae).
