Originally Posted by Byron
If your viewing schedule doesn't match up, another trick is to have the lights on for 5-6 hours, off for 1-2 hours, then on again for 5-6 hours. This is said to inhibit algae because the period of dark in the middle doesn't allow them to make full use of the light whereas plants can so they are unaffected.
Alga are a simpler organism than plants, and are photosynthesising much quicker than plants at lights on. What happens with the siesta is that the CO2 levels have the opportunity to build back up again for the next lights on period. This works fine in lower light tanks, but all it is proving is that the tank is CO2 limited.