You will probably be testing after equilibrium and if you are using mixed bed or really clean DI water, you will need to get a resistivity meter, as for testing the water.
DI water if cleaned properly has very little conductivity in it. There is a ASTM method of added some salt STANDARDS to your water then testing it. Many companies try and test without these salts and end up with erroneous readings from their meters. They think the meter isn’t working when virtually, the meter just can’t function with this water cleanliness.
At a pH of 7, very nearly half will be in the bicarbonate form radical, HCO3 -.
It will be rather meaningless as the line is near vertical at pH water theoretically should have a pH of 0 -giving it an equilibrium of 10^-7 hydrogen ions and 10^-7 hydroxide ions,. As it sits in open air Carbon Dioxide will absorbed resulting in Carbonic formation Acid. Generally, it would take very little absorption of CO the pH drop from 0 in water as it absorbs Carbon Dioxide.
Several commercial pH meters are precise enough to measure accurately within this pH range assuming the meter is properly calibrated. Don’t worry too much if you see the pH drop in the water as you measure it -this is natural as explained above. If your initial readings are around 7 then drop to no lower than ~ 5 -you have good water. Now look. Perhaps a better way to test your water is to measure the conductivity. You can also measure for total dissolved solids, chlorides, and alkalinity in the water. For example, electronic meters are available commercially to measure conductivity and TDS. Test procedures exist for checking chlorides and alkalinity.
DI water to be ~5 is because of the carbonate system that gives off protons.
To eliminate CO2 in DI water, I bubbled N2 gas into DI water. By the way I observed the water pH go past What is making the pH of DI water to surpass pH of 7, as I continued to bubble N2 gas into DI water. I’m sure it sounds familiar.|Doesn’t it sound familiar, this is the case right?|Sounds familiar?|doesn’t it, am I correct? if for some reason you must have a pH of very nearly 0, you may want to consider a mixed bed polishing tank.
Here is some theoryH2O molecules have infinite resistance.
It is ions that cause solutions to be conductive. Even perfectly pure water has some ions equilibrium because between H2O, H+, and OH-. The ions concentration H+ and OH in perfect water is 0000001 molar at 25º The pH of this water is exactly difficulty Because in the accurate measurement of pH in ultrapure water, ASTM has at least removed the requirement from the specification for Type I and Type I deionized water. Perhaps you could point your Aerospace customer to that specification and convince them to remove the pH limit or to replace it with a resistivity limit.