The BOROUX Proactive Fluoride Filter is an add-on filter designed to reduce up to 99% of fluoride from your drinking water. It uses an alumina-free, dual-layer nano-carbon filtration system with a patent-pending upflow design that increases contact time for more effective filtration. Each pair filters up to 1,000 gallons of water and is housed in durable stainless steel shells for long-lasting use. These filters attach to compatible upper chamber filters, including BOROUX Foundation® Filters and Black Berkey® Elements, and are installed in the lower chamber of your gravity water filtration system.