They look similar in scale/shape to other aiptasia I've seen, but the tentacles and coloration looked a bit different. Wasn't 100% sure on the ID. I'd estimate them to be 1/2" to 3/4" across.
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Looks like it, I would glue it in if you can. It spreads like wildfire if you attempt to pluck it. Peppermint shrimp in a lower flow area can eat it, in a higher flow zone a file fish would work better.