I'll treat him with aquarium salt. How long should I do this for? In an earlier post you said keeping them in salt for a long time wouldn't be good. I don't mean to be a hard-headed or anything, but I keep Orlando, my sick boy, in Epsom salt for two days sometimes and he comes out much better. It might just be my luck though, and I wouldn't know about aquarium salt.
Remember what was said about worrying your fish to death? How many times have you treated that poor fish?
Sometimes when a fish is stressed from moving to different environments and being over medicated the fins will get ragged. It may not be fin rot or anything but stress. If he has been treated he will either live or die. I know this is harsh but that is the way it is with fish.
You should strive to set up a living ecosystem, not a chemistry set. This is the hardest lesson for a beginner to learn and sometimes it takes years.
I am not trying to put you down because most of us have been through it and we lose a lot of fish in the learning curve.