Help identify and solve

[dlh]

I thought I'd won the hair Alge and now this. It's grey and fuzzy. I brush it off the rocks and it returns in days. I don't have a clue as to what it is and I need help and guidance getting rid of it. Yes, my parameters are all within range. Thanks in advance for any help!

 

[Mechano]

Maybe try putting some under a microscope and someone might be able to help identify it better.