Laying some Kalkwasser paste on em usually kiils them but if you don't get all of it they will return, I have some in my smaller tank that I keep in check that way. I had a File fish in my bigger tank and he took care of all the Aptasia and then hopped in my overflow and that was the end of him. Too bad I was getting attached to the little fella...... Be Aware !!They do tend to nip at other corals...at least mine did..