RODI filter changing

[bigfoot86]

I've had an BRS 5 stage RODI unit for almost 8 months now. Was wondering how to know when change out the filter in the cannisters and the resin. The resin has changed from black to brown by about 75%. The TDS meter still reads a zero for the outflow.

 

[AZDesertRat]

Here are some threads where this is discussed in great detail:
https://www.reef2reef.com/forums/eq...ation/81125-reverse-osmosis-deionization.html
https://www.reef2reef.com/forums/eq...on/117953-ro-de-ionization-filter-change.html

You need three TDS readings to troubleshoot a RO/DI system, tap water TDS, RO only TDS before the DI and final RO/DI TDS. You also need to make sure your TDS meter is clean and calibrated. I never trust color changing resins since they are very inconsistent and dependent on how well they were blended, stored and packed in the cartridge.