The main tank replacement filter for the Optim H2O whole house system is made with an ultra-dense, 0.5 micron-rated carbon block filter. Catalytic carbon and activated carbon are combined to perform superior filtration for first-of-its-kind effectiveness. Shield your home from lead, cysts, PFOA/PFOS, chlorine, chloramines, and more for one year or 100,000 gallons of use. Compare to Pelican Water, Express Water, Spring Well Water Filtration Systems, Ne Aqua Systems, Bluonics, Hardless NG, Culligan, APEC Water Systems, i Filters, & More!