The water softener filter extends the lifespan of the humidifier. It is compatible with model AD 7971. The filter can be rinsed periodically from the outside under running water. The replacement time depends on the hardness of the local water. It is recommended to replace it every 1-2 years. The filter is made from Maifan stones, a natural silicate mineral. The Maifan stone is a composite mineral or healing stone that is non-toxic, harmless to organisms, and has specific biological activity. Its main chemical composition includes inorganic silicate aluminates such as SiO2, Al2O3, Fe2O3, FeO, MgO, CaO, K2O, Na2O, TiO2, P2O5, MnO, and others. Keep out of reach of children.