Increasing TDS between DI filters

ti_lavender · Jul 15, 2023

I have a 3 stage di setup that I’ve been using for 6 months. It’s the BRS cation/anion/mixed bed setup. I just replaced all three medias with brand new unopened single size packages. I did my initial run after the replacements and I’m seeing an increase in TDS by 8-10 from incoming to the unit compared to after the cation/anion stages. Previously the first 2 stages can take it to 0 and the third is more a backup. Has anyone have experience or insight in to if I got bad media?

KStatefan · Jul 15, 2023

Mine alway takes a few gallons until it goes to zero when I replace resin

Randy Holmes-Farley · Jul 15, 2023

An anion or cation only di filter SHOULD raise tds as they swap ions in the water for H+ and OH-, both of which are more conductive than any other ions that they replace. When water passes through both, the H+ and OH- combine to form water and the conductivity drops again.

ti_lavender · Jul 16, 2023

I’ll try running a few gallons through to see if the tds goes to zero.

Randy Holmes-Farley said:
An anion or cation only di filter SHOULD raise tds as they swap ions in the water for H+ and OH-, both of which are more conductive than any other ions that they replace. When water passes through both, the H+ and OH- combine to form water and the conductivity drops again.

The TDS meter I have reads before the cation and after the anion so I should still see a net reduction.

Randy Holmes-Farley · Jul 16, 2023

ti_lavender said:
I’ll try running a few gallons through to see if the tds goes to zero.

The TDS meter I have reads before the cation and after the anion so I should still see a net reduction.

Yes, after both, when both are working perfectly, it should be zero, but since you have a mixed bed after that as well, it’s ok that it is not.

it may soon be time to replace one ir both if the single bed stages.