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Hi, welcome to the site!
...Red macroalgae. It's too small of a sample for me to really tell which one...it could be gracilaria or botryocladia. I have it all over my snails, it won't hurt them but if you have corals you won't want that red algae...it spreads everywhere.
We don't have coral yet but I'm sure hubby will want some. Ill let him know.