Berkey PF-4 Fluoride and Arsenic Reduction Elements for the Berkey Earth Filters or Ceramic Filters The PF-4 is for use with Berkey Ceramic Filters - If you use Black Berkey Purifiers, you will need the PF-2 Primarily Filters Fluoride and Arsenic Attaches to the bottom of a Berkey Ceramic Filter - Used as a Post-Filter For use with Big Berkey, Travel Berkey, Berkey Light, Royal Berkey, Imperial Berkey, Crown Berkey