OP1L Lead, Cyst, PFOA, and PFOS Replacement CartridgeReplacement cartridge for RKIN OP1L Certified Whole House Lead, Cyst, PFOA, and PFOS Treatment System. Recommended replacement every 100,000 gallons or every 12 months, whichever comes first. Please follow the filter replacement instructions available by clicking here. The reset button is very small and very easy to miss; please see the photo below for the exact location of the filter reset button. Press and hold for 3 seconds to reset the filter