To receive optimum performance with your Nikken products, replace filters and other components when necessary. Your product manual includes the recommended intervals for inspection (where applicable) and replacement. This may need to be performed less or more frequently, depending on operating conditions. Gravity Filter cartridge: 6 months or 528 gallons (2,000 liters), whichever comes first* Gravity Mineral Stones: 1 year or 1,056 gallons (4,000 liters), whichever comes first* *Component life may vary, depending on water quality