Although delicate to keep, longnose butterfly will do a good job on aptasia.
Get a needle and shoot them with a dosage of calcium, directly into them. That wipes them out the quickest.
On a sad note, over the weekend, lost my friend of nearly 13 years. Had him nearly as long as my dog Champ. He was around 18" long. I figured him to be well over 20 years old when he passed.
He was a very, very, very rare New Caledonia Emperor. Nothing much seems to come from that part of the world any more. What made him unique from New Caledonia was the deepness of the blue color and the streamer on his tail.
Will miss my buddy and his grunting.