Show us a picture. If you're talking about glass anemones and not aiptasia or majanos, leave them be. I have tones of the glass nems, they don't hurt anything and look cool. They only stay in dark places and only open at night. They don't sting any corals.
I suspect they are good for a tank and I believe them to be filter feeders or eating uneaten food in a tank.
I had gotten a peppermint shrimp when I had aiptasia and within 48 hours all were gone. The 1st night after lights went out I peeped into the tank and he was going to town on them.
+1 on peppermint shrimp for aiptasia. Worked like a charm. Just be careful with whatever else is in your tank. Peppermint shrimp like to pick and feather duster worms may be eyed by the pep.