24 Hours before a planned drain and refill remove cartridge filter elements and soak in Natural Chemistry's Filter Perfect. Do not reinstall filter elements until Spa Purge process is complete. With spa water temperature @ 95 degrees or higher, circulation pump running and jets off, add entire contents of 1L Spa Purge bottle to spa water. After 20 minutes, run jets a minimum of 1/2 hour. The next day, drain, rinse and then refill spa and reinstall filter elements. Proceed with normal spa maintenance.