Question Is It Normal For Ro/di To Make Water That Has Ph ~5?

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bitseriously

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I have a ~2 month old 4 stage RObuddie unit. On a lark, I tested the water it’s making today for gh, kh and pH (don’t have a tds meter, it’s on my wish list).
Both hardness measures were near zero (1st drop colour changed). The pH tested at ~6 on API kit, and ~5 on Nutrafin kit.
I know test kits are best thought of as approximations. Ie not super precise or accurate. Best taken with a grain of salt. But that seems like a really low pH to be coming out of RO unit, doesn't it? (Not a rhetorical question).
My tap water is ~8 pH (right out of tap), and moderately hard.
The ro unit is ~2 month old, and I make 5-10 gal per day, on average. It’s a bottom of the line 50gpd unit.
The DI resin is changing colour, but not yet depleted (I think - I’m new at this). Bottom half of di canister is orange, top is brown-blue.
Does all this pass the sniff test?
Thx!!!
 

ryanr

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Hi,
"1. The pH of totally pure water is around 7 (with the exact value depending on temperature). As carbon dioxide from the atmosphere enters the water, the pH drops into the 6’s and even into the 5’s, depending on the amount of CO2."

"2. The pH of highly purified water is not accurately measured by test kits, or by pH meters. There are several different reasons for this, including the fact that highly purified water has very little buffering capacity, so its pH is easily changed."

Scroll to the Final Effluent pH section
http://reefkeeping.com/issues/2005-05/rhf/index.php
 
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