Berghia are terrible options IMHO. They will starve to death after they are done. A much better option (and just as fool proof) is to make a thick paste out of rodi water and kalk and cover the aptasia you see with it. Get yourself 10 or so peppermint shrimp (saltwaterfish.com is having a sale right now) and put them in your tank. The shrimp will eat any small aptasia, you knock out the ones you can see and whaaaalaaaaa, no aptasia and no inhumane treatment of critters, you net yourself some additional cleanup crew AND ITS CHEAPER!!! BAM!