definately need brighter lights and more plants to soak up nitrates...what are you water parameters...ph, ammonia, nitrites and nitrates? you need a test kit like the api test kit to check them...what fish are in the tank? you are probably getting algae from the brignt window behind it...maybe pull the shades ... perhaps a ligh filtering shade would work or close the drapes...too much sunlignt on a tank can cause algae...you also should do 50% water changes every week...