There are a few ways now to eliminate it. There is a chemical method developed called
Aiptasia X using this follows application and safely destroys it. I have had no use of this and cant really comment on if it is worthwhile.
Being a reefer though i feel this method in appropriate. I prefer tying to sort things out the natural way. The purchase of a peppermint shrimp or two depending on tank size works really well from my experience and gives the addition of an invertebrate to the tank.
There is a third that i have recently heard of called Berghia Nudibranch these are available from HB aquatics and can be ordered online, But unlike the peppermint shrimp once all the aiptassia has been consumed these will dye out, this is not good for the conservation of this hobby. But HB Aquatics will buy back the nudibranch and then can be sold to another reefer and continue another feed of aiptasia.