Aries (AF-20-2115-BB) 20"x4.5" Big Blue 1.5 KDF-55-GAC FilterAries Filter Works 20"x4. 5" Big Blue AF 20 2115 BB KDF 55 GAC Specialty Filter Dual action filtration combining coconut shell GAC with KDF 55 media for whole house chlorine removal, heavy metal reduction, and bacterial inhibition KDF 55 & GAC Whole House Heavy Metal Reduction WHY IT WORKS Redox media meets activated carbon for extended performance KDF 55 Redox Process Removes chlorine and reduces water soluble heavy metals through oxidation