Powder blue tangs tend to be generally a peaceful fish, in comparison to many other tangs and even other Acanthurus species. In the wild, large adults can be a bit aggressive, but they typically travel in large groups in the wild. Singularly in aquariums, I have never had any major issues with them as far as aggression. Most people usually have issues with Zebrasoma tangs (yellow, purple, sailfin, etc.) and the other Acanthurus tangs like clown tangs and sohol tangs. They do get fairly large though, and require a large tang because they are constant swimmers.