A 125 gallon or larger aquarium is necessary to provide plenty of swimming room. It is aggressive towards its own species or tangs in general, and best kept with only one per tank.
Although Tangs will eat meaty foods along with the other fish in the aquarium, it is important that they are offered plenty of marine based seaweed and algae. This will strengthen their immune system, reduce aggression and improve their overall health.
Source: Live Aquaria - Photo used as indicative only.