Marks, PLEASE stop acting like a moderator. Yer always making these annyoing comments to people, I always see em. "you post too much". "stop copying posts". "Stay with one thread". Just cut it out PLEASE. Try to be helpful???
Anyways, nice fish. Although they ARE pretty, they are pretty much one of the largest species of tang, "Sailfin" tang, for a reason, lol. It will become roughly the size of a medium dinner plate given a full life span. You will definitely need a much bigger tank. BUT, i see that you have plenty of coralline growth so the tank seems to be healthy. Give a couple months, then get a larger tank, or trade in the fish. Also, plenty of algae. Did u name it?