I bought Melafix but it was too late. You can get it at Petco. I noticed recently that Manhattan Aquariums was carrying something (forgot the name, there is '2' in it) that I had read a lot of good things about.
No matter what, you will need a small QT tank.
Note that since this is a very sensitive and shy fish, I would recommend that when you put it back in your tank, you first let it inside a protected enclosure for a couple of days, that way he gets used to the tank, and its inmates will not see him as food when he is released back in.