Heads up for a long post
First...what type of live rock do yo have? Any Pacific version..ie, Tonga Branch. There are two varieties of Aiptasia..one that muiltiplies like crazy, which looks like the one you have, or others form the gulf or atlantic that are still Aiptasia but do not take over the tank. Peppermint shrimp will work on small Aiptasias as long as they are the Pacific variety shrimp...Peppermint shrimp from the east and gulf coast do not recognize Aiptasia as a food source...hence the hit and miss problem.
Here is another recipe for Aiptasia euthanasia. Take 1 teaspoon Kalkwasser powder, mix in two tablespoons water...microwave for about 20 seconds. Use a syringe, I got mine in the puppy feeding area of Petsmart...10 cc. Stir the Kalk mix and suck it up into the syringe. It helps to wet the rubber seal first before sucking up the Kalk mix...allows the plunger to slide more easily.
Make sure you turn off your pumps before going Aiptasia hunting. They are going to retract as soon as they feel the start of the Kalk but just coat the hole or crevice. Be careful of coral nearby as the concentrated Kalk will kill them as well..you have to have good targeting ability..get the tip of the syringe as close to the place where the Aiptasia is hiding. Wait about 20 minutes or so before turning your pump(s) back on.