If you can remove the rock from the tank, you could try taking it out and scraping off the Aiptasia. Then a drop of bleach to kill what doesn't come off and rinse/soak in salt water before putting the rock back in your tank. Don't try to remove it while still in the tank or it will spread. Depends on what else is on the rock and what it can handle. I have never had much luck "injecting" them with chemicals.