Simple way to kill aptasia. Mix up some kalkwasser-inject it directly into aptasia with syringe. The kalkwasser's exothermic reaction burns the anemone from the inside. Fatal 100% of the time. Oh and fill the anemone up with kalk. Dont skimp of the kalkwasser. Easy, simple, effective with zero negative effects on the tank. Plus you dont have to throw away a perfectly good coral frag.