You have to kalk them. Then again. Then again. Then again about five more times after you cannot see any more.
A harsh angelfish like a Queen can get 'em, but they also can get other stuff. This might work in a SPS-only tank and I have considered one to eat all of my Z&P but I like my clams too much to risk it. If you have no other fleshy stuff, then this could work. It would be my luck that I would get the 1 queen angel in 20 that is a good reef citizen.
The aiptasia killing stuff is usually kalk and lemon juice or a strong acid like diluted muratic. If the warning label does not want you to use too much at once, then it could be diluted muratic acid. If it is white and settled, then it is probably just kalk. Some of the kalk ones have some lemon juice or other mild acid in them.