As for the antibiotics, I am not aware of any that I would recommend as antibiotics can and will kill the filters at doses less than those needed to cure the fish. On the off chance that it is parasites, a regimen of 3 treatments with Proform C with either Fluke M or Prazi added to the last dose would address the possibilty of it being a parasite issue, but if that doesn't work then you still need antibiotics which will require catching the fish. Once you have caught it, if you have a suitable container for an isolation tank, then that makes catching much easier.