The Pool Frog® Mineral Reservoir contains a proprietary blend of minerals and fits inside the Cycler of the Pool Frog® Mineral System. The minerals continually replenish themselves for added protection against bacteria and algae, as well as keeping your pool's pH balanced by acting as a neutralizer. One Mineral Reservoir will last the full season or up to 6 months. Use two reservoirs for year-round pools. For use only with the Pool Frog® Mineral Inground Pool System or the Pool Frog® Mineral Above-ground Pool System.