While low levels of phosphates will not harm your fish, plants or invertebrates, high levels of phosphates will lead to algae blooms. Levels of 1.0 ppm are favorable for algae growth and at 2 to 3 ppm, algae growth is very likely to occur (seephosphate test kits). Ideal phosphate levels are 0.05 ppm, or less.
Phosphates come from a variety of sources: uneaten food, dead fish, decaying plants, tap water & fish feces. To reduce phosphates limiting the sources is key. Using RO water will help if your tap water has phosphates. Frequent water changes (easily done with a gravel vac)will reduce phosphates quickly, but it may not take care of the underlying cause. If phosphates persist, the aquarium phosphate removers on this page will help to reduce your phosphates. Some of these products will require the use of a media bag or a reactor.