Well My betta reacted just fine. I had to continue the treatment as directed so her immune system wasn't compramised so if you do add fin rot medication Make sure you do the full treatment. Do you have a pic of your betta fish's tail? He could be tail biting which I actually had one of my bettas do. I'm sure if you post a thread about it (If you haven't allready) Someone will be able to infer if it's fin rot or not :)
I saw you mention in a thread that your mom put fin rot meds in your betta's tank when she obviously didn't have fin rot. How did she react? Did it bother her at all? I'm somewhat certain that my Poseidon has fin rot, but I'm not absolutely positive and I don't want to wait a bit to see because then it could be too late and I'm terribly paranoid... So I want to go ahead and treat him, but if he doesn't have fin rot and it's just assorted damage from the evil walmart cup would it hurt him? Did it bother your betta?