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DI Resin is necessary to reduce Total Dissolved Solids (TDS) to zero and is the last stage of an RO/DI unit. It is not necessary to use the expensive proprietary DI cartridges that other RO manufacturers sell. Simply buy a refillable DI cartridge if you don't have one already and fill with DI resin. You'll save money and get the same results.
Nuclear Grade Mixed Bed DI Resin