Jusy slowly squirt them with it i can usualy kill 2 or 3 with one syringe full.
boiled water worked great for me.
I actually just used hot tap water and a toothbrush on the rock that had the problems and just scrubbed the area with hot water. havent seen any more since then
John
90 Gallon Reef Tank
15 peppermints in a 20 gallon fuge with a ton of aiptasia = aiptasia gone overnight.
5 peppermints in a 150 gallon tank with a few aiptasia = aiptasia gone in a few weeks.
kill all the aiptasia that you can find and introduce several peppermints (with the lights out so they can work without getting eaten).