This “Compatible” Humidifier filter removes mineral and pollutants from water. Filter discoloration is natural and will carry depending on water. Replace filter about every two months (depending on use and local water quality) or when performance starts to deteriorate. Help keep your humidifier clean and extend filter life by using other Honeywell accessories including antibacterial treatment (HAC100). This helps control bacteria and algae growth in your water tank, and provides odor free operation for use in evaporative humidifiers only.