Hi, I’ve been dealing with this stuff for a few years. It’s constrained to my sump but it’s stubborn and had a penchant for growing directly in the middle of zoa colonies. Treated for bryopsis over the summer. Didn’t do anything to stuff. I also have a tomini tang/hermit crabs and snails and they don’t touch the stuff either. Open to any ID and suggestions for removal. To this point doing manually had kept it in check but I’d like it gone.