Pull the rock out, taking note of which hole the aptasia is coming out of, then pack kalk into the hole. You don't need very much, less than half a teaspoon. Then just place the rock back in the tank.
kalkwasser powder.LFS should carry it..dont take the rock out.when it opens up use something like a syringe or small baster to squeeze some in its mouth when its opened.mix the kalk with water till its pastey
i didn't think of it much when i first saw it in my reef tank. it has gone wild on my tank the aiptasia-x does work great but they do still come back , so take it from a very frustrated person take care of it NOW even if you have to take that rock out
I've had success with white vinegar+ a syringe. 2 came back in the same spot, but I think they may have started to close before the vinegar had gotten into their mouths. Definitely turn the pump off while you're injecting, though. Good luck!