Something doesn't sound right. With that amount of dissolved CO2, I would've expected the pH to be lower than neutral. If that's not enough CO2 to drop the pH, then CO2 is probably not the issue.
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I'm just doing some follow up, in case this helps any one.
I just added a booster pump to my RODI system. I'm running my RO membrane at 80psi. It is taking my incoming water TDS from 1120 down to 3 after the membrane. My DI is polishing off the 3 TDS and the life of my DI is greatly increased. Prior to the booster pump installation I was getting 60 TDS after the membrane. If anyone is having difficulty getting TDS low I strongly recommend trying a booster pump