Is this a flatworm or something else. I am getting something I’m assuming flatworms on my mushrooms. I can blow them off and after awhile a couple will come back. Also I can see them swimming when I blow them off. Not sure what they are.
Looks like it could be red planaria flatworms. The flatworm itself isn't the issue, it's that they will reproduce very quickly and cover everything, blocking light to your corals.
Are they rust colored?