The Aqua-Pure™ AP431 replacement cartridge is designed to reduce hard-water build-up on hot water-using appliances such as water heaters (standard and tank-less), clothes washers and dishwashing machines, and plumbing fixtures like faucets, pipes, and shower heads. By reducing scale buildup, the life of hot water systems, pipes and downstream plumbing fixtures is extended.Designed specifically for use with Aqua-Pure™ AP430SS system, the AP431 uses polyphosphates to inhibit hard-water scale buildup.Product Benefits:Designed for scale and corrosion inhibition to help extend life of hot water systems, pipes and downstream plumbing fixturesIdeal for any size home and light commercial applicationsMulti-application design effective on all types of hot water systems - including boilers, tankless, and tank-type (gas or electric), as well as whole-house and commercial humidifiers.