JennM;1027907 wrote: Yep those are some beefy Aiptasia. You likely won't get rid of them all at once. If you do manually remove as many as you can, even a piece of leftover tissue will regenerate, and when they are stressed with chemical removal, they can release their gametes which will cause a whole new crop.
If you don't have any fish that are prone to eating invertebrates like shrimp, I'd consider getting a bunch of Peppermint Shrimp - they will help keep them in check if/when they grow back.
They're a nasty nuisance.
Jenn