PF-2 reduction elements are designed for use in conjunction with Black Berkey waterpurification elements to adsorb the following unwanted elements found in drinking water.? Fluoride? Arsenic V and pre oxidized Arsenic III? Other residual heavy metal ionsTECHNICAL INFORMATION:FLUORIDE: Testing for fluoride was based on 20-30ppm of the ion in the influent aqueous solution at a flow rate of nomore than 3 gpm per cubic foot of media. Results of 95 reduction). Under optimum conditions, effluent concentrations of less than 50 ppb were readily achieved( 99.75 reduction).ARSENIC: This product uniquely targets the entire family of arsenic oxide anions as well as the arsenic cations.REPLACEMENT:Under normal conditions it is recommended that each set of two PF-2 elements be replaced after 1,000 gallons (The BerkeyLightTM system is about 2.75 gallons therefore the PF-2 filters should be replaced after 363 refills. If the system is refilledabout one time per day, the PF-2's should be replaced annually, if the system is refilled about twice per day, the PF-2'sshould be replaced about every six months).