i have the same thing, it's orangish brown and sticks to gravel really well, my theory is thats what hydras hatch from, i've been told hydras are harmless and show you have good clture, although it's ugly. ANy advice on getting this out is appreciated. hydra (as I know them is a small squiggly line you see moving in the tank, i'll see a lot when I stir up certain parts of the tank, usually areas under logs where the water is still, seeing your pic looks like what I get though.