Was I the last person to learn how acidic DI water will get? I have struggled with pH in the 7.8 range pretty much since I set up the first tank. On a lark the other day, I tested the DI water before mixing salt. It read <5.0!
I get water from an industrial sized DI tank unit we use at my company. On demand, unlimited supply. VERY clean water. I called the company who supplies the units, and they fully expected a 5.4 reading. Said "if you measure it IN LINE you will get 7.0 water, but as soon as you expose it to air it will start absorbing CO2, converting it to carbonic acid."
This is the same process as acidification of the oceans we read about. Apparently DI water has no minerals to buffer the water, so even small amounts of CO2 will significantly drop pH. I fill my buckets very violently in an attempt to super-oxygenate the water, cuz - why not? That has helped introduce even more CO2 to the water. Hence readings even lower than they expected.
I have been dropping pH with every top off! I think my water changes did less harm cuz the salt mix added buffers. Now, I buffer the fresh water to 8.3 or so, and my pH is holding steady. I HATE learning stuff the hard way!
DI water is not acidic, it is neutral or close to a pH of 7.
You cannot accurately measure the pH of ultrapure water, this is well documented.
DI water quickly takes on the pH of whatever you add it to or is added to it.
Unless you are adding massive quantities the pH shouldn't change noticably. If you are seeing changes then it would be better to top off more frequently with smaller quantities since the pH of the DI will be around 7.
Last edited by AZDesertRat; 07-07-2013 at 05:28 PM.
Again, read up on why you cannot test the pH of ultrapure waters, its meaningless. There are literally hundreds of good scientific articles on the subject.
DI Water and pH
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