Fin rot is a term used to indicate a bacterial infection on the surface and around scales--it's not a specific bacteria. Any injury or stress can cause the lowered immune response that allows the bacteria to get in. I would treat with an antibiotic, like maracyn, instead of the fungus medication, since the maracyn is broad spectrum and more likely to kill the pathogen. It will also wipe out the beneficial bacteria, so be prepared to do lots of water changes during the course of treatment, until the tank can re-establish.
