Hydro-Logic ARCS Replacement Cartridges#741608 ARCS Stage 1 Replacement Poly Spun Sediment Filter reduces rust, silt, dirt, sand and sediment. Change every 5,000 gallons of product water. #741610 ARCS Stage 3 Replacement pH Neutralizing Remineralizing Cartridge to balance out and stabilize the pH. Replace every 10,000 gallons of product water. #741612 ARCS Stage 2 Replacement Heavy Metal Reduction Cartridge to remove heavy metals. Replace every 10,000 gallons of product water or as needed.