Pentek WS-20 Water Softening Filter Cartridge, 20" x 2-1/2" Reduces hardness minerals and scale deposits in low flow rate residential and commercial applications Cation, sodium-form resin ion-exchange media with polypropylene pre- and post-filters Capacity of 1500 grains Recommended flow rate of 0.75 gpm Maximum temperature of 100 degrees F (37.8 degrees C)