sludge

I noticed this white, sludge-like, white thing among my rocks, does anyone have an idea of what it could be?

Why does Cyanobacteria get such a bad rap? I haven't dealt with it personally. From what I read it creates Cyanotoxins, steals oxygen, which in itself is bad. But people make it seem like it's the biggest nightmare of their lives! I've heard it can be caused by a multitude of reasons, ranging...