Try adding a Peppermint Shrimp, I had one that helped me deal with a persistent Aiptasia problem. I was also using a syringe and Kalk or lemon juice to kill the big visible ones, but they kept coming back until I added a peppermint. Copperband Butterfly or Filefish would also help, but a peppermint shrimp is usually cheaper and more readily available. Just make sure you get a real peppermint and not a camel shrimp or something else similar looking.
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