What are these?

[Beverly]

Yup. Aiptasia. I inject them with calcium supplement using a needle tipped one ml syringe. Vinegar also works, but it will lower pH. Inject 2 or 3 times at various angles to make sure you get the syringe tip into the aiptasia once it shrivels up when you approach it. You may have to do this one a few occasions if you don't inject it properly the first few times. No big deal. Just keep after them.