Aries (AF-20-3202) 20"x2.5" Anion (Hydroxide Form) Mixed Bed DI FilterAries Filter Works Professional Grade Deionization Aries AF 20 3202 20"2. 5" Mixed Bed DI Filter (Hydroxide Form) Anion mixed bed resin cartridge for laboratory grade water purity in whole house and well water applications requiring final TDS reduction to near zero 20" 2. 5" Standard Mixed Bed DI Resin Hydroxide Form TDS Polishing WHY IT WORKS Ion exchange resin removes dissolved solids that carbon and sediment filters cannot touch Mixed Bed Ion