The Tetra DeepBed tertiary filtration system provides superior total phosphorus removal to limits below 0.2 mg/L. Rounded sand grains with a sphericity of at least 0.8 are used in the system and a 6-ft media bed allows for up to 2 lb of solids per square foot of filter surface area before backwashing is required. The sand media sizes in the 2- to 3-mm range and a maximum uniformity coefficient of 1.4.