The pep shrimp worked, but then I thought they were starving in my small tank so I took them out. After many months the aps came back and the next shrimp I put in didn't touch them.
Using a hypodermic needle I tried injecting each stem with lemon juice or vinegar; both worked great but was very diffuclt to do. I bought some kalk (about a cup container) at the lfs for $14 and mixed 1/4 teaspoon and put one drop on the center of each ap. That worked too. I then found out that Mrs Wage's pickling lime at Walmart, for more than 2 cups for $2, was the same thing.
Try Mrs Wages, she's good. Make a paste, as thick as thin pancake batter. I used a syringe to carry the drop of paste to the aptasia and deposited one drop. Don't slop it around. It is very white and will kill coraline which took about two weeks to recover the white spot.
The paste will quickly form a very thin shell on the drop when the drop touches water, so it is easier to use than you may think. The thin shell will hold the drop until you deposit it on the ap. At $2 you can't go wrong. I got my large syringe at Walmart too; it main purpose is to inject liquids into turkeys to keep them moist as they are cooking. (A small hypodermic can be bought at a feedstore or vetinary supply.)