I‘m gonna try chiming in again. Hopefully it goes better than the first time I asked questions to try assess the situation. Not sure if you were taught this or researched it somewhere, but why are you doing nitrate testing on your source water and RODI product water? The more important measurement to make sure you get optimal performance from your RODI is a TDS reading. Total Dissolved Solids is how you determine how free your water is from contaminants. Most likely, your RO Buddies did not come with them. It’s a good idea to get at least a handheld TDS-3 meter, which is temperature compensated, for a more accurate reading.
You want to take 3 readings.
1) From the Tap
2) After the RO membrane but before the DI resin
3) After the DI resin
After the DI resin should read 0 TDS. The tap water reading and post RO reading will tell us how efficiently your RO membrane is operating and will help determine how we can maximize the efficiency of your RODI system based on your source water.
Once you are mixing saltwater with 0 TDS RODI water, we can eliminate that variable and move onto the next. Based on this thread, the elimination of this one variable is just the tip of the iceberg. There seems to be much left to learn and do IMO.
