Aries (AF-20-2012) 20" x 2.5" (2 lb) KDF-55-GAC FilterAries Filter Works 20" x 2. 5" Specialty Filter Aries AF 20 2012 KDF 55 GAC Filter Cartridge High capacity redox media and activated carbon filtration for chlorine removal, heavy metal reduction, and bacterial control in whole house and well water systems 2 lb KDF 55 22,000 Gallon Capacity Bacteriostatic WHY IT WORKS KDF 55 and GAC work together to extend filter life and improve water quality Redox Filtration KDF 55 uses oxidation reduction chemistry