For heavy aiptasia infestations I recommend the aiptasia eating filefish. Ive had 2 in my tank for about 4 months now and they wiped out all the aiptasia and have never touched another coral or invert (and i have feather dusters and critters all over my live rock). the first week I didnt notice many aiptasia gone, but over the next 2 - 3 weeks they ate every single one in the tank.
I was skeptical at first, but I also knew the aiptasia would kill off my corals too so...but ive been pleasantly surprised, and now that the aiptasia is gone they just hang out in a cave most of the time and come out when i feed and will eat anything from frozen to hikari algae tabs. And they also change colors/patterns quickly and ive seen them mimic just about every color in my tank from purple, to green, to orange and yellow.
Not everyone is brave enough to try, but they're cheap and effective and love to eat aiptasia.