I just registered here today, but have had a reef tank for almost a year now. When I got it, the former owner (several years established) had lost interest and let the tank sit under a burned out light for over a month. She told me that probably everything in the tank was dead. I got it home, set it up with some decent lighting and it began to come alive. There was one hermit, one Nassarius snail, three mushrooms and a few rock critters on about 35 lbs. of live rock (20 gallon long tank). Within weeks, I started seeing lots more signs of life... micro brittle stars, pods, sponges and on and on! Then, after a couple of months, I notice the dreaded Aiptasia growing on one of the rocks... and then another. I ordered a product called Aiptasia Rx and used it religiously for three weeks. It was a complete waste of time and money. I removed the two pieces of rock and squirted lemon juice right down the throat of those pests with a syringe. Then I took some pointed tweezers and removed them from the rocks, trying to take some of the rock also, to prevent leaving any of the pests behind. Then I soaked the spot again with lemon juice, rinsed in fresh water and put the rocks back in the tank. Thought I had completely eradicated them until a couple of weeks ago. I noticed some sprouting in one of the spots I had treated and another colony in a new location. That's when I decided to get a peppermint shrimp. He has been in the tank for a week now, and I see no change. However, I have added livestock that did nothing but hide for over three weeks (a Royal Gramma), so I'm going to give that one lonely little shrimp some time to prove himself. The Aiptasia is on top of the rock and the shrimp hangs out under the rock. So, I can't tell you what works, but at least you know some things that won't work.
I built a 20 long sump/refugium 6 weeks ago with the intent of adding a Green Mandarin Dragonet (commonly called a goby). My main tank is absoluitely teeming with pods, and now, so is the sump. I think I have a healthy enough population to support the Mandarin, but I am hoping to see the shrimp work on the Aiptasia before I get one. The pest is nowhere near being out of control or threatening the few corals I have added. I just hate to see it at all. My other livestock includes an Ocellaris Clown, two Orbiculate Cardinals (not PJ's), a Green Clown Goby who likes to sit atop my Frogspawn, half a dozen hermits and as many snails, some Green Button Polyps, Green Star Polyps, a Kenya Tree, several more mushrooms and thousands of other rock dwellers. I still want to add another Clown, a Small Blue Tang (for algae control) and the Mandarin. I know... I am maxing out my capacity. That will just give me more incentive to build a bigger tank!
I wish you the best with your Aiptasia. IMO, the best route is natural control as opposed to attempted eradication... but I am no expert!