Are they growing from a mat? They look kind of like Blue Clove polyps IMO. These are the absolute worst and can be extremely hard to get rid of. They just keep popping up here and there regardless of what you try and remove them with.
Looks like the ones we have. Like blue clove polyps but more brown in colours. I've tried to find an animal that would eat those polyp, but not even our corallivore butterfly fish touch them.
They didn't like Fenbendazol, but I would not recommend treating the whole tank with it.