TDS Meter

I purchased an HM Digital DM-1 dual in line TDS Meter from Bulk Reef Supply and received it today. A TDS meter is used t measure the amount of Total Dissolved Solids in RO/DI water. My RO meter is about 14 months old so I figured it was time to check on the performance of the filter. Since it is a dual meter it allows me to check on both the tap water and RO output. If I want I can place the first sensor between the RO and DI sections but haven't done that yet.

My water input measures 313 ppm. The output of the RO filter was measuring 60 ppm, not great when the goal is 0 ppm. I have never flushed the membrane so I went ahead and flushed it for about 45 minutes. I also positioned the two DI canisters so they are vertical instead of horizontal. This ensures that the water goes through the beeds not over them. After flushing and running the RO filter the output is now down to 8 ppm of TDS. Much much better. I did notice that the beads in the two DI filters are now dark. The second filter is much darker than the first which makes no sense to me. It's probably time to replace the resin.