I've had aptasia, and had success with two methods of elimination:
1) Copper banded butterfly fish - they love it, but are often susceptible to being bullied and withering away. They require frequent feedings of mysis mostly. Also, they are sometimes caught with cyanide and often fail to fully recover, only to wither away after a few months. They may pick on some corals, too, so you need to be careful with them.
2) Peppermint shrimp - I have three now in my 90 reef, and they got rid of the aptasia 100%. My understanding is taht there are a few differnt types of peppermint shrimp, so be sure to make sure you get the right kind.
Some people will get rid of the aptasis with a kalkwasser paste, but I prefer to do it through mother nature.
Agree with Water Keeper - get rid of the aptasia asap. They will cost you time, $, and be a constant source of aggravation.
AP