Well, if you have a serious infestation, then a chemical based strategy may be your only chance of salvation. It's really not recommended to use chemicals in the tank, especially if you have coral, but if it has gotten to that stage where it's just getting ridiculous, then it may be your only choice.
You should go online or to your LFS and find a chemical product that is designed to eradicate aiptasia, but would do minimal damage, if any, on the other inhabitants of your tank. Also, if you decide to use chemicals, i would say be ready to do some serious water changes after you've waited the proper amount of time with the chemical in the tank to kill the aiptasia. Also be prepared to keep a close eye on your coral when you use the chemical to see if they begin to react badly to the chemical and show signs of any amount of stress. And if they do, LARGE WATER CHANGES. Do them immediately to prevent further damage on the coral. Also be aware that most aiptasia removal products contain very harmful products, even if they claim that they don't. Most of those chemicals are designed for FOWLR tanks with no coral, so there is little to harm when the chemical is introduced, so you need to do some serious research on the chemical you plan to use, and search for testimonials from other people that have used that product as well.
BEWARE: Do not try and crush or rip off the aiptasia as that will only spread them around your tank even more. You would have basically fragged the aiptasia and they will spread even faster. The torn apart pieces are like seeds and will spurt new aiptasia growth elsewhere in the tank.
Hope this helps.