Can DI water have non-neutral pH?

Hash and Stuff Extraction
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1

I installed an under sink RO water filter system (5 stages) plus a two stage mixed bed cation/anion exchange resin; it works great inline and has read 0 ppm dissolved solids. However, when I check the pH, it reads 5.3, which doesn’t make sense to me. There’s no ions in solution that could do that since they all got balance out with the ion exchange gel and the only ions left would be H+ and OH-. I also have a nice pH meter that I recently recalibrated.

Is there a hole in my logic here or am I correct and I’m missing something on my setup like too high flow or a calibration issue

2

Distilled water and RO water are always acidic. This is because pure water has no buffering capacity and as soon as you put it in contact with the air, CO2 dissolves in it, creates carbonic acid and lowers the pH. The pH of DI water is therefore generally in the 5.2-5.5 range depending on purity of the water and CO2 concentration in the environment.

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