Blue-green algae / cyanobacteria? Or is it something else?

I think I have blue-green algae in my tank (cyanobacteria). The problem
is that it's not green at all. It's brown in color. It seems to behave
like blue-green algae because it's usually in the spots with little
water movement, on the gravel and hanging on anacharis/elodea and
surrounding my hairgrass. It's like brown spiderweb hanging on the
plants. On the gravel it looks like some fuzzy stuff. I know it's not
hair algae because I have some hair algae on my anubias.