New Water In-Ground Cycler Pac comes pre-filled with 6.16 lbs of chlorine and easily inserts into the New Water System. They also last much longer than chlorine in typical feeders due to the erosion design that limits how much chlorine gets wet at one time. For use with New Water series 400 and 600 in ground cyclers. Also fits Pool Frog XL Pro series 5400 cyclers.