Aiptasia is a fast-spreading pest anemone that stings corals and multiplies rapidly — and scraping it off only spreads it, so it's removed by predators or targeted treatment.
Peppermint shrimp (the real Lysmata wurdemanni) will eat it, but identification matters and they may ignore it if well-fed. For reliable control, spot-treat each anemone with a dedicated product rather than trying to cut them out.