Aptasia-X has somewhat worked for me. Sometimes though it seems like you treat a couple and then 10 more pop up. The last time around (about a month ago) I put twice as much as normal and left all the pumps off for an extended time (30 minutes+) -- left an air bubble going after a while.
I think that, and having an Aptasia Eating Filefish, have worked to control my population.
I still have 4-5 I know of, but they are in caves I can't easily get to.
I haven't actually seen the Filefish actually going after any Aptasia. When we got it the fish was really small, between a nickel and a quarter. It's gotten bigger since then; hoping it's at least keeping any new ones from spreading, and that as it gets bigger it will maybe go after the bigger ones in the caves.