Quote Originally Posted by alton
My DI units don't last very long (200 gals.)so I put my TDS meter in front of the DI so I can monitor when my charcoal and micron membrane start to get bad. If you have the drinking water attachment or water polisher to the end of your RO unit this will add things back in. Aquariumfilters.com answers many of these questions.
Your sediment filter and carbon block have negligible effect on the total dissolved solids. Read/record/monitor tds levels in three places:
1. tap water
2. after RO but before DI (to monitor performance of your membrane)
3. after DI (to monitor performance of your DI resin)