Phosphate limiting was a popular idea that was brought about from the PMDD article. Now-a-day's that is considered as an old way of thinking. Many members of this board have high levels of both No3 and Po4 and have no algae. With today's high tech tanks, No3 and Po4 can get used up in a day. The idea is to grow plants as much as you can to eliminate algae. If you limit the plants, then the algae will spread because they can utilize the other levels in the water.