Peppermints will chow it down.
Problem is, there are 2 very similar looking types of peppermint shrimp. I'm not talking about camelback's either. Try to do some research on the different ones, IIRC it's something about the pattern of stripes. The true Peps work best if you put them in isolation like a small tank then put the rock in question with them.
I had a couple zoa rocks that had 20+ Aps on each and put them in a small tank with 12 Peps. Aptasia gone in 2 days. Left them in for an extra day to clean all up and have never seen another one on those rocks.