Using a syringe, inject either lemon juice OR Better yet, kalkwasser powder mixed with ro water into a paste the consistency of toothpaste into the CENTER core of the aptasia and watch it melt
I know this thread is several weeks old by now, but I thought I’d let you know that I got a peppermint shrimp and a few days later all my aiptasia was gone, and I haven’t had a problem with it since.