Aquatic Life Spot-Free Car Rinse Unit & Dual Deionization Systems for Aquariums Cation and Anion resins (H+ and OH-) remove the remaining total dissolved solids (TDS) from membrane-filtered water The resin changes to white or tan color when media is exhausted Includes 2 - 10" Mixed Bed Color Changing Resin Cartridges (Item No.330091) The Dual DI System has 0.5" and 0.25" connections for multiple plumbing applications Included mounting brackets and wrenches make installation and maintenance easy!