Yellow and purple tanks in my experience are aggressive to any tank mates that can’t hold their own. Both of mine have punished their weaker tank mates. They even fought each other until I had to remove one and take to a larger home.The aggression in the case of purple tangs and most zebrasoma is limited to other tangs. So, if a purple tang was to be your only tang in this tank you should be fine. Some acanthurus tangs, particularly powder blue tangs, will often bully anything and everything. Although purple tangs can be nasty they also can do quite well with other tangs if added simultaneously. But once established and "tank boss", be weary! @Ryan15236