Phosphorus is usually present in natural waters as phosphate (PO4-P). Organic phosphate is a part of living plants and animals. Phosphorus is an essential element for plant growth, and a fundamental element in the metabolic reactions of plants and animals. In most waters, phosphorus functions as a growth limiting factor because it is usually present in very low concentrations. the natural scarcity of phosphorus can be explained by its attraction to organic matter and soil particles. Any unattached or free phosphorus, in the form of inorganic phosphates, is rapidly taken up by algae and larger aquatic plants. Because algae only require small amounts of phosphorus to live excess phosphorus causes extensive algae growth called blooms. Algal blooms are a classic symptom of cultural eutrophication.

Phosphorus can be found in sources of human waste, animal wastes and industrial wastes. Shallow and very slow-moving waters are most vulnerable to the effects of cultural eutrophication. Phosphorus stimulates the growth of rooted aquatic vegetation. These plants in turn draw phosphorus previously locked within bottom sediments and release it into the water causing further eutrophication. The advance stages of cultural eutrophication can produce anaerobic conditions in which oxygen in the water is completely depleted. These conditions usually occur near the bottom of a lake or impounded river stretch and produce gases like hydrogen sulfide unmistakable for its rotten egg smell.

The effects of phosphates in your aquarium are, as with other types of water pollution, a shift in aquatic life to a fewer number of pollution tolerant species. better put the fish who cannot tolerate this environment will die. Species that can tolerate low dissolved oxygen levels are those such as carp, midge, larvae ,tubifex etc......