I've had good success with aiptasia-x not only for aiptasia, but for majanos as well.. from what I've read it's primarily sodium hydroxide (NaOH, AKA lye), which is very effective when applied directly over the nuisance anemone (it exhibits an intense localized heating reaction, plus is very strongly basic), but you have to be careful about overspray, as it can be irritating to other animals if you get it on them, plus large quantities of it can affect SG, as it releases sodium as it reacts .
It's definitely something to use with care, but in my experience works very well as a last resort when used according to the label directions.