The POOL FROG Twin features two Cyclers in one installation. One Cycler holds the Mineral Reservoir that destroys bacteria all summer long and the other holds a 4 lb. Pac that precisely dispenses the small amount of chlorine needed for each pool. This complete system of minerals and a LOW level of chlorine creates Fresh Mineral Water for pools up to 25,000 gallons. POOL FROG Twin does the work automatically so you can relax. Simply replace the Mineral Reservoir every 6 months and the FROG Pac every 3-4 weeks when empty.