Here is a good analogy for why aiptasia is considered a "bad" thing in a tank. Lets pretend that the aiptasia is a dandelion and your tank is your front yard. At first you find two or three and they are "kinda cool", but then a week later you have no grass (or in the tanks case coral) and you have about a thousand of them. Then your yard (or tank) looks kind of trashy and run down. Thats the best explination I can give.
I agree with Mike here, I would look into the product that he has mentioned, as most "miracle potions" are just to get people to spend more money at the LFS. Joes Juice, and Lemon Juice work great, I have used both methods on my brothers tank.