Try boiling RO/DI water and injecting it into the aiptasia. Then you can use a baster to suck up any loose pieces. This is how we keep our in check. Just a thought (and cheap one too!).
Yea, from what I have heard peppermint shrimp are pretty much hit or miss with these guys, but on the plus side it adds some more life and movement to a tank.
peppermints work well, but if your not looking to get another life form I have used Joe's Juice with great success,just dont accidentally squirt it on anything else in the tank. I ruined a colony of zoas that way.
I put 20 peppermints in my tank & had no luck at all. Think my Hawk fish might have eventually killed the peppermint shrimp! Haven't seen any in awhile.