This stuff is slimy, dark brown, doesn't blow off rock, only way I can remove is by scraping with a blade. Its in the sand as well, first thought was amphidinium, but my tank has always ran nutrient rich. Snails and inverts don't seem to be affected by it. I run chemipure blue as well. I thought cyano but all my experiences with cyano has been they easily blow off rock surfaces. So now I'm thinking lyngbya, but again its not hair algae. . . I did put scraping in water and hydrogen peroxide, water turned brown not pink. . ..