The Berkey PF-4™ Fluoride and Arsenic Elements should be replaced every 1,000 gallons or at six-month intervals (whichever comes first) under normal conditions. If your water is heavily contaminated with MTBE, fluoride, lead or arsenic, the filters should be replaced in four-month intervals.
Please note that high or low pH impedes the ability of the media to reduce fluoride. For maximum fluoride reduction efficiency, maintain the water being treated between a pH level of 5 and 7.