If you want to get rid of Aptasia fast, easy and chaep, get some Joe's Juice. It runs around $7 - $8 that will last a LONG time. It is easy to use and works great. I even read one review of it where they treated Aptasia on a rock that had yellow polyps all around and not a single ployp was lost.
The best thing about it is that you apply it directly to the Aptasia, not the whole tank.
I used to get rid of some in my tank that I picked up on some stuff from a local coral shop. Worked first time and no issues.