Pool Algaecides by Pool RX. Details:Pool Rx+ [Pool Rx Plus] is the updated algaecide formula from Pool Rx. Pool Rx+ contains three active ingredients, Copper Sulphate, Zinc Sulfate and Silver Nitrate, adding additional layers of protection to the original Pool Rx formula you have come to trust. The blue Pool Rx+ pool unit is an EPA Registered, NSF/ANSI 50 Certified, swimming pool algaecide supporting 7.5K-20K gallons of water. Pool Rx+ reduces chemical demand, improves water quality, simplifying pool care for up to 6 months. The Pool Rx+ pool unit is effective in rejuvenating the Pool Rx+ minerals for up to 1 year in your pool. For best results, start with a new Pool Rx+ pool unit at the beginning of each swim season. For year-round pool use, add a Pool Rx+ booster after 6 months, or if you see algae coming back sooner.