Murray,
I have stuff like you are describing in my 120g. Not at all fuzzy and looks like coraline, which fooled me at first, but I think it's still a cyano species.
What makes it so funny to me is that the oldest fossils found in Pre-cambrian rock (edit: about 3.8 billion years ago) is of cyanobacteria and here were are today, all us smart folks, trying to rid our tanks of this super-ancient life form
