Ouch, I hate to say this Marie but those look like the little buggers
The ones in my tank were a little browner in color but hydroids just the same.
They can give off a powerful sting, which eventually can kill sps
corals. I had two areas of rock where the hydroids were actually
matting underneath two sps bases that were about 4 inches in diameter.
I was advised to remove them if the growth patches were small and confinned,
if they are spread throughout the entire tank I would
probably take a more drastic approach and get new rock
