I have aptasia for years, only takes 1 bad rock or a frag from the LFS
Clean them out is almost impossible, Berghia Nudibranch, Peppermint Shrimp and Copperband Butterfly
are the natural way to control them.Non of this worked for me, couldn't by Nudibranchanywhere locally, shrimps got eaten by Trigger fish, Butterfly strawed to death since he was a picky eater.
I stop buying Aptaisa-X, since it will only kill the one successfully injected with it. Kalkwasser seems to me work fine, use small dose at a time, also I use RO
water to mix Kalk
Cleaning your tank out probably will take months, have to be proactive and get the mix ready as soon as you spot one, don't wait for 2-3 or 10.