The MediaGuard Cartridge System provides for high-performance filtration in water softeners. Utilize KDF-55 in the MediaGuard System for reduction of chlorine and heavy metals. For reduction of hydrogen sulfide and/or iron-laden water, use KDF-85 in the cartridge system. As a rule-of-thumb, choose the 4-cartridge system with KDF-55 for city water applications and the 6-cartridge system with KDF-85 for well-water applications. One drum of KDF will fill twelve 4-cartridge systems or eight 6-cartridge systems. Use the Accessory Kit to fill cartridge systems. These systems are for downflow use only.