Aptasia Eating File fish. Ive used aptasia X, works, but wont fully get rid of it and it will come back. Copperbands are good, but finding one that will eat aptasia and frozen foods can be troublesome.
Ive had the best luck with the aptasia eating file fish, but then again this can be hit or miss. You can get one that will nip at coral, or one that is reef safe, but does not eat aptasia, I think I got lucky with mine, he eats aptaisa as well as frozens and has never bother a coral yet, but i keep watching. LOL