WS Series cartridges provide softened water in a convenient cartridge-style design. These cation exchange softening cartridges utilize a bed of sodium form cation resin beads to reduce hardness and scale deposits. The convenient and space-saving design of our WS Series cartridges means that softened water can be provided easily and cost effectively at the exact point of need. WS-20BB cartridge has a rated capacity of 4,500 grains (as CaCo3)capacity. Model Grain Capacity (total TDS) Dimension Flow Rate WS-20BB 4,500 GPG (77,000 PPM) 4-1/2" x 20" 2.00 GPM Specifications: Filter Media Standard Softener Resin End Caps Polypropylene Shell Polypropylene Pre-filter Polypropylene Post-filter Polypropylene Gaskets Buna Temperature Rating 40F to 100F