I use a mix of sodium hydroxide and kalk. I use lab grade sodium hydroxide, though I have heard that other grades of lye are sufficiently pure. I turn off all my pumps and use a syringe. It forms a sort of thin gel in the water which helps keep it in place. I cover whatever aiptasia I see and let it sit for an hour, then turn the pumps on. It all gets blown into the water and I've never seen an adverse reaction in the tank. I wouldnt recommend doing too much at one time, though, since it can always lower your pH. It doesn't rid the tank permanently of course.
In any case, like the other guy said about sodium hydroxide, it's not for the feint of heart. Nasty stuff. It'll dissolve anything living. Aiptasia, corals, fish, your eyes, your skin, etc.
I might try peppermints.