It's also ALWAYS based on individual fish. I've seen Copperbanded butterflies and Morish Idols live for years where most of fish, couldn't keep them a month. I've seen various angels live among corals with no problems and others that can't put any corals near them. Tangs in general seem to have most of the weird quirks about them, with aggression, feeding habits, and immunity. If you have one of those tangs that seem to pull through regardless. You got him for a steal. Too bad they don't breed, I would say to get them a mate and sell them for $1,000.