I can tell by looking at it that it is a rabbitfish not a tang. They get big, very hardy and tough, also very peaceful. Be careful however as its Dorsal and I believe anal fins are venomous. They are vegetarians and will eat algae, macro-algae, and spirulina.
Although they get big, you shouldnt have an issue having a 240 as they dont get that big.
Man thats an awesome looking rabbit though, not very common either.