I've had my baby RES for about 5 months now and he has a few basking rocks, but for awhile now they've started growing a dark green substance and I don't know what it is. It comes off with a light wipe of a rag/scrubber, and the only other things I have in the tank are smooth glass rocks covering the bottom, a pump and a fake plant. The pump also gets the green on it where the water consistently runs over it. Anyone else have this problem/know what this stuff is?

- The dark green comes off in flakes