The Pentair FNS Plus 48 sq. ft. Fiberglass D.E. Pool Filter provides the highest level of filtration. The FNS Plus is capable of filtering out particulate as small as 5 microns. That's the same size as a human red blood cell. The FNS plus uses a set or grids coated in pool grade diatomaceous earth. The set of grids consists of 7 full grids 24" in length and 1 partial grid 24" in length. The FNS Plus tank is made with fiberglass-reinforced polypropylene that enhances durability and product life. It uses a hi-flow manual air relief valve that eliminates air buildup in the tank rather than having it force back thru the system. A 1-1/2" drain is used for quick drainage, and a steel tension control clamp rests securely around the tank, a brass barrel nut securely fastens each half tightly.