Gosh man, i didnt get a real chance to look intel now. He is really beat up. You want my suggestion? I would suggest getting another QT. Since i know this wont happen as you probably dont have the $$$ and you dont have another filter to strap onto it. He really needs the least amount of stress possible and obviously the other guys are giving him trouble. I would start with meatflix soon. Also Water changes will help a ton as if it is Columnaris It thrives on waist and water changes will help. The thing is stress is a big factor in getting fish better and these guys are giving him trouble. Maybe get larger cheap rubber bin to put them in and make a tank divider is what i suggest unless you have another filter to strap onto another tank or bin so he can be by himself.