Many researchers have studied the relationships of phosphorus, nitrogen and algae. When they examined thousands of samples of algal biomass from different locations around the world, they found the ratio of nitrogen to phosphorus to be remarkably consistent. Regardless of location, type or origin, the ratio was very similar and ranged between 14:1 and 17:1 Nitrogen to Phosphorus. This relationship is called the "Redfield" ratio".
Where Phosphorus forms insoluble compounds, Nitrogen forms very few insoluble compounds and is removed via biological processes utilizing naturally occurring bacteria.
What this means in a real world example is that when 31 pounds of phosphorus is removed, 200 pounds of Nitrogen cannot combine or grow about 3000 pounds of algae which would contaminate over 1.4 million gallons of water
The phosphorus removal process converts any ammonia and ammonium ions to nitrite and nitrate. In an environment of substantially reduced phosphorus concentration, the denitrifying process is more effective resulting the best possible water quality improvement