Hopefully your peppermint shrimp have taken care of the aptasia by now. The above mention aphasia-x works fairly well. There are other similar products available...joe's juice comes to mind. Some folks use the smother method, that is covering them with an epoxy and either leaving it in place or removing it few days later. I have tried all of these methods and they all work to a degree. The shrimp worked the best for me. Unfortunately, my large A. percula decided the shrimp were put in the tank as food and took great delight in devouring the shrimp. Eventually, the aptasia returned and I purchased a copper band butterfly. No more aptasia, but I do watch the butterfly to make sure it hasn't decided that some of the corals look good enough to eat. So, decide which method you want to use and hang in there.