2 AUTHENTIC REPLACEMENT BERKEY PF-2 FLUORIDE AND ARSENIC REDUCTION ELEMENTS FOR BERKEY GRAVITY-FED WATER FILTER SYSTEMS, INCLUDING: Big Berkey, Berkey Light, Crown Berkey, Imperial Berkey, Royal Berkey and Travel Berkey Systems. FLUORIDE AND ARSENIC REDUCTION- Berkey PF-2 Fluoride and Arsenic Reduction Elements replacement filters are designed for use in conjunction with Black Berkey Elements to adsorb fluoride, arsenic(V) and pre-oxidized arsenic(III), and other residual typical heavy metal ions. THE ORIGINAL "PF-2 FILTERS" BY BERKEY- Berkey is still the one and only manufacturer of authentic Berkey PF-2 filters which have been proven and tested to effectively remove fluoride when used in conjunction with authentic Black Berkey Elements. Don't fall for lookalike filters that use our Berkey PF-2 model number or trademarks in their titles or product descriptions to legitimize their brand as replacements or "compatible", when they are not. LONG LASTING- We recommend replacing Berkey PF-2 Fluoride and Arsenic Reduction Elements after 1,000 gallons of use, under normal conditions. EASY TO USE- Berkey PF-2 Fluoride and Arsenic Reduction Elements attach to the bottom of Black Berkey Elements and sit in the lower chamber of a Berkey system.