The best way to gauge when to replace the Berkey PF-2™ Elements is to do the following:

1) Keep a track of how many times per week you need to refill your system.2) Then multiply that figure times the capacity in gallons of your particular system (for example the Berkey light™ system is 2.75 gallons) to determine Total Gallons Used Per Week.3) Finally divide the Total Gallons Used Per Week into the 1000 gallons and that will tell you how many weeks before the filters should be replaced.4) Next calculate the future date for replacement (52 weeks per year) and write that date on a sticker and attach it to the bottom of your system for future reference.

By the way, if you have been using your fluoride reduction filters for some time now, you can still use the above formula to determine when to replace the filters. Just count forward from the date you purchased your filters.