I noticed this about a week ago. At first I thought maybe it was just from him fighting with one of the other fish So I just put some salt in and left him alone. It still hasn't healed up at all but Doesn't seem to have spread much at all. I don't think it is a parasite since it really hasn't spread or spread to any of the other fish but I'm not to good with parasites so I don't know. Was thinking maybe it is a bacterial infection and melafix could be the problem? Or maybe it really is just a "skin rash" from fighting with the other guys. maybe someone could help he's still eating like a monster and swimming around without a care in the world.