Four Black Berkey (BB9) Replacement Filters & Four Berkey Fluoride Water Filters (PF2) Four Black Berkey Filters (BB9) & Four Berkey Fluoride Filters (PF2) Black Berkey replacement filters will fit the following systems: Berkey Light, Big Berkey, Royal Berkey, Imperial Berkey, Crown Berkey, Travel Berkey. Berkey Fluoride Filters (PF2) attach to the Berkey Black filters (BB9) and reduce fluoride and arsenic. PF2 filters and are compatible with all Berkey water filter systems. Each Berkey filter element has a life of 3,000 gallons: Thats an incredible 6,000 gallons for a two-filter system and 12,000 gallons for a four filter system! Each set of two Berkey PF-2 fluoride water filters should be replaced after 1,000 gallons (3,785 liters).