Humidifier filter removes minerals and pollutants from water. Filter discoloration is natural and not proceed according to the water. Replace the filter every two months (depending on use and quality of local waters) or when performance begins to deteriorate. Helps keep your humidifier clean and extend filter life by using other Honeywell accessories, including antibacterial therapy (HAC100). This helps control bacteria and algae growth in water tank and provides an odor-free operation for use in evaporative humidifiers only.