1 part system: Top half treats water for 6 months and bottom half chlorinates up to 4 weeks. Easy mineral sanitizing pool care. Bacteria fighting minerals. Bottom half chlorinates up to 4 weeks. Plop it in and wait until it flops. Dosage: Adjustable chlorine output (8 settings). No touch chlorine cartridge. For refill use Model No. 4401, (SKU 800137).