Here is the number one problem with aiptasia is that even if you kill the big ones you will still have small babies. They release their eggs into the water and they grow faster than algae. I would suggest removing anything valuable (like fish, crabs...ect) Turn off your skimmer and remove all carbon from your tank. Than you want to make it snow in your tank. Spike up your calcium, kh, ph and saltwater to stupid levels. I had my saltwater at .40, calcium over 600 for 2 weeks (I don't remember the other levels). When you have high levels of calcium it will look like snow in your tank. Than I did several water changes and turned my skimmer on and put my carbon back in. I waited 2 weeks and did another water change. I waited a month for my tank to go through another cycle. These things are mean and nasty and hard to kill. This method does have a potential to kill your good bacteria. Luckily for me it didn't. I had to go to these extremes since I was not about to buy new rocks for a 150 gallon tank. The only other option is throwout everything, clean every part of your tank with vinegar, and get new sand and rocks.
