About granular activated carbon water filter cartridge20'': The GAC/UDF Filter Cartridge uses NSF/Coconutshell/Coal granular activated carbon, good at removing odor, color and chlorine. The activated carbon used has been processed by acid-washing and wind-selection and the end caps are fixed with special PP layer instead of general non-woven cloth. So no carbon fines coming out.  At the same time,it keeps a high flow.   We use auto-filling machines, not labors, to fill the granular activated carbon filters.  The weight tolerance is small and have higher efficiency.