Well I know this will be hard without a photo but my camrea took a ooh: On one of my snail shells the is a grey anemone thing. I did remove it cause i am paranoid. So you are thinking whats the issue... I think I have spotted one on my rock. Is it a pest??? Aiptasia? BTW it was really hard to scrape off the snail shell even with a razor blade. I did google an image of aiptasia it is similar but not as tall and shorter tenticles.