Cartridge 9306B is designed for the reduction of taste, odor and aesthetic chlorine during the prefiltration stage in Kinetico drinking water system Plus Deluxe VX and GX models, k2 by Kinetico drinking water systems, Purfecta drinking water purifier, Aquakinetic A200 and K5 drinking water station. This cartridge should be replaced each time your system's MACguard Filter (postfilter) shuts down (around 500 Gallons of water), you should replace your prefilter and postfilter cartridge at least once per year. Cartridge 9309A is designed for the reduction of sediment during the prefiltration stage in Kinetico Drinking Water System Plus Deluxe VX and GX models, K2 by Kinetico Drinking Water Systems, Purefecta Drinking Water Purifiers, AquaKineic A200 & K5 Drinking Water Station. This cartridge should be replaced each time your system's MACguard filter shuts down. In K2 by Kinetico Systems and AquaKinetic A200 without MACguard, you should replace your prefilter and postfilter cartridges at least once per year.