3 Layer Filtration systems: The outer layer adsorbs impurities; the ion-exchange resin in the middle layer heavy minerals, such as calcium; and the inner layer traps additional impurities before the water is released Replacement Cycle： For a better, we recommend that you replace the mineral cartridge about once a month Applicable models: suitable for HM512S, HM612S, HM713, HM713S, HM813S, HM717S These Humidifier Demineralization Cartridges ensuring safe and water and effectively saving you time and money The demineralization cartridge hard water, the formation of scale and white for a more comfortable humidification