And this water filter also compatible with our AQUA CREST Gravity Water Filter System, Model No.: AQ-TN-A-FS. The water filter is not sourced by or sponsored by Berkey. Longer service life: To achieve optimum performance, replace the black filters every 6,000 gallons per pair and replace the fluoride filters every 1,000 gallons per pair, which will vary based on water conditions.