If it was the Copperbanded Butterfly,( never heard of a CB tang) There was already a strike against him. They are probably only second to Moorish Idols at being the worst in captivity. They don't feed well and very prone to disease. Not that I blame you, I have had both only to lose them in a week. If you find one that will eat, they get sick, if you find one that isn't sick, they wont eat.