Use a syringe commonly found in Salifert test kits. I use no needle.
I boil a cup of tank water in the microwave, and inject a syringe-full
into the hole the aiptasia lives. I repeat this several times. Have
NEVER had to repeat this procedure more than once to get rid of
aiptasia. 100% success. Just did this a couple of days ago to some
aiptasia that came on a zoanthid rock-aiptasia no more. Of course be
careful of anything close by, although I have never killed anything
other than aiptasia. The zoanthid within 20 mm of the aiptasia was
not even harmed.