Aries (AF-20-4202-BB) 20"x4.5" Big Blue Twin Bed Mixed Bed DI FilterAries Filter Works 20"4. 5" Big Blue Twin Bed Mixed Bed DI Filter Nuclear grade deionization for ultra pure water production in whole house and industrial applications AF 20 4202 BB 20" x 4. 5" TDS Reduction WHY IT WORKS Twin bed mixed resin technology removes dissolved solids to near zero TDS Mixed Bed Ion Exchange Cation and anion resins work together to capture dissolved minerals, silica, and ionic contaminants that carbon and sediment filters miss