Removes: Fluoride, Arsenic V and pre-oxidized Arsenic III, as well as other residual heavy metal ions. * It is recommended that each set of two PF-2 elements be replaced after 1,000 gallons. As an example, The Royal Berkey system is about 3.25 gallons and therefore the filters should be replaced after 307 (1,000/3.25 ) refills. Or in other words, If the system is refilled about one time per day they should be replaced after 10 months, if the system is refilled about twice per day they should be replaced about every 5 months. * You simply screw the PF-2 Flouride filter into the Black Berkey filters. * We do not bundle these as our price is so low, however you can order as many as you like