I have red coraline algae that looks like what was shown in the picture. This is not the same thing. It's hard not slimy and doesn't rub off. I used a bristle brush and it stayed. I got new live rocks about three weeks ago with some of this stuff on it. One rock had a huge, ping pong ball size area, and since this discovery I've found tiny areas here and there on at least four rocks that cropped up over those three weeks.