OK, Water/RODI experts...question


New member
I have and Optima 4 stage RODI unit from purelyH2O. The system is probably 10 years old, but I just replaced everything in the beginning of March...the sediment filter, carbon filter, DI filter, and RO membrane. I ordered this: http://purelyh2o.com/index.php?page...tegory_id=57&option=com_virtuemart&Itemid=103 with the 1 micron option and 75gph RO membrane. I have made about 20 gallons a week...about 160 gallons total. My output TDS has just gone up to 001. My input TDS is ~155. It seems like the filters should last a lot longer than this, right? What would I need to replace to get it down to zero again? Are they subpar filters they are selling? Do you think I should contact them?


New member
If you are testing after the DI 1 ppm is a big deal, you need to change the DI

Try testing the TDS after the Membrane and you should have at least a 97% rejection rate, with your feed water that should be below 5ppm. You DI should be lasting a lot longer

Elevated CO2 levels will cause shorter DI life. The Spectrapure Page on RC has a lot of good info in the stickies

Randy Holmes-Farley

Reef Chemist
Premium Member
Are you measuring TDS inline, or separately?

If the latter, 1 ppm is not a concern.
If the former, and it used to be 0, then it may indicate DI depletion and I'd watch it carefully.


New member
It seems from your post that you're measuring TDS of the incoming tap water and the final product water. You might want to temporarily switch your meter's measurement points to measure your tap water and the product water coming out of your RO membrane (but before the DI resin). You should see at least a 90% reduction in TDS after the RO membrane.

If not, I would check to see that the RO membrane is fully seated in the housing, and that the rubber gaskets aren't deformed.