De-ionization post-filter cartridges have a mixed bed of color changing DI resin. The housing is translucent so you can see the resin color. The cartridges reduce phosphates, nitrates, silicates and TDS. Change filter when media changes from green to orange. Cation and Anion DI resins 50/50. #741614 is 10 in x 2.5 in and has maximum of 0.25 GPM flow rate for an estimated life of 7,500 ppm. #741616 is 10 in x 4.5 in and has maximum of 1 GPM flow rate for an estimated life of 18,750 ppm.