Pool Frog XL PRO In Ground : uses a Mineral Reservoir in one Cycler and a pre-filled Chlorine Pac in the other, for complete pool care with x-tended chlorine pac life over the regular In Ground POOL FROG®. This allows you to have more fun with your pool and spend as little maintenance time as possible. With minerals, chlorine use can be cut up to 50%* over standard water treatment programs. This is a very convenient way of reducing chlorine use and hassle. The XL Pro does the work automatically while you and your family experience an endless summer.