The PoolRx Black Unit supports 20,000 - 30,000 gallon pools. PoolRx is an easy to use algaecide that reduces chemical demand, improves water quality, lasts for up to 6 months, and really works! PoolRx contains a proprietary blend of minerals that continuously and effectively eliminates algae. Simply pick the correct sized PoolRx unit based on total gallons, clean your filter first, then, drop the PoolRx unit into the pump basket or skimmer. The specially treated alloy cylinder is packed with the PoolRx mineral formulation. These minerals immediately dissolve out of the cylinder and form a stable residual throughout the pool water for up to 6 months. The minerals eliminate the algae while freeing up low levels of chlorine to be more active and productive in the water. During the pools filtration process the minerals are rejuvenated every time they return and pass through the cylinder. PoolRx works synergistically with a constant low level of chlorine. Residential (0.5-1.0ppm); Commercial (1.0-5.5ppm) If needed, a PoolRx Booster (part# 102001) can be added for longer seasons, larger pools or tough condition. The PoolRx unit is effective in rejuvenating minerals for up to 1 year in the water, so start with a new PoolRx unit at the beginning of each season for best results. PoolRx has been simplifying pool and spa care since 1994 and can support any size body of water. PoolRx is also ideal for Salt Pools.