The NFGAC-20WH, Nelsen 20" GAC Big Blue Filter is a filter that has granular activated carbon that helps in the effective removal of chlorine. It removes the bad taste and odor due to the presence of chlorine, organics, and bacteria. The filter measures 4 1/2" x 20? and has a capacity of 25,000 gallons. It has an impressive flow rate of 5 psi and a temperature range of 40 F - 125 F. The filter is NSF Certified for material requirements.