Yum, green water. I got hit with that one too. I got rid of it by having the light on only a few hours a day for a week or so. Of course it just recently came back, but that's because I stirred up all the gravel a lot redoing the tank (I'm guessing). I have more plants in there this time so hopefully it will be gone soon.
Edit: Yes, it's an algae bloom typically called "green water"... I wasn't just describing your water.