As mentioned above, that window is causing the algae bloom. UV sterilizers, stronger pumps and diatom filters will only clear up the algae that is floating in the water column but if you don't take action to limit the amount of light the tank gets then the algae will start to take over on any surface in the tank.
i had this happen to my old 75 gal. tank was placed well away from a window, finally found that when the bulb had burned out, it had mistakenly replaced it with one of my high uv bulbs for my reptiles, changed the bulb and alge cleared up within a couple water changes.