I have a rock or two in my tank with some weird algae on it. It looks just like the purple coraline algae but it is burgundy. I'm worried that it might be cyano, but it hasn't grown on the sand, it just grows on the rocks. It starts out looking like cyano on the rocks and I am able to scrub it off, but after a while it encrusts the rock. Unlike the purple coraline algae, it is also slick/slippery. I read in a book that it is 'peysonnelia sp.' and the picture looks pretty accurate. It says that the algae is rare and found at depths of up to 650ft, and you would be lucky to get a hold of this algae. If that is true, then I don't want to get rid of it, but I'm worried it might be bad for my tank. Anyone else have this?