I guess that makes sense as far as it being moss. I just associated it because it was right after I put those rocks in and they had moss on them when I cleaned it off. My tank isn't near a window but I do have a heat lamp and a 15 watt tropical uvb lamp. I had both on for 14 hours a day for a while because the tank was too cold and my RES had a respiratory infection. I brought it back down to 12 hours a day but is that still too much 'sunlight'. I just clean it about once a week maybe once every two weeks depending on how bad it gets. I don't mind the algae just as long as it doesn't hurt my turtle. He's my pride and joy. Thanks for the feedback and any additional comments are appreciated!