Count the elements in your upper chamber now and replace like for like. Most Travel, Big and Royal owners run 2 elements, which is 1 set. Imperial and Crown owners often run 4 or more for faster flow. A Big Berkey holds up to 4, a Royal up to 4, an Imperial up to 6 and a Crown up to 8. More elements means faster filtering, not cleaner water, so 1 set is a fine place to start if you are unsure.

Yes. Every Berkey stainless system, whatever year you bought it, uses the same mounting hole, wing nut and washer. Phoenix elements were built to that spec. If your system took Black Berkey elements, it takes Phoenix elements. If you have unused holes, keep the blocking plugs in place as before.

If you want fluoride and arsenic reduction, yes. PF-2 filters thread onto the bottom of each Phoenix element exactly as they did on Black Berkey elements, one PF-2 per element. They are rated for 1,000 gallons or one year, whichever comes first, so if yours are older than that, replace them at the same time. If your water is not fluoridated, you can skip them.

A set of 2 Phoenix elements is rated for 5,500 gallons, which is 3 to 5 years for most households. Replace them when the flow rate drops and does not recover after scrubbing the outside of the element under cold water, or when the red dye test lets color through. Phoenix elements carry a 1-year filter warranty. The lifetime warranty on your Berkey covers the stainless chambers and hardware.

The same way you primed your Black Berkey elements. Use the PrimeEasy primer that comes in the box to push water through each element until it runs out the other side, install them, fill the upper chamber and run the included red dye through once to confirm the seal. The full priming guide has photos for every step.