Handheld pH probe

[Hobster]

I have a Milwaukee pH hand held pen. Why does the manual state : do not store in ro/di water, but to use bottled drinking water? Is that because the bottled water is close to pH of 7. What would happen if stored in tap water of a higher pH of 9.5 or in the ro/di ?:) Thanks

[Boomer]

Hob, it is best to store it in a storage solution, which is a weak acid. I'm sure you don't have any, so it is best to store it in pH 4 Buffer. Don't store it in RO/DI

[Randy Holmes-Farley]

One reason to not store it in RO/DI water is the driving force for ions to diffuse out of the glass electrode into the low ionic strength RO/DI water. Drinking water has a higher ionic strength, so there is less driving force for the glass to lose ions to the solution.

You might also just use 1 part tank water to 5 parts RO/DI water.

You may find this article helpful:

Measuring pH with a Meter
http://www.advancedaquarist.com/issues/feb2004/chem.htm

[Hobster]

Thanks Randy and Boomer. Would the 1:5 mix be better than the drinking water which is 6.9 to 7? Also isn't the" pH 4 buffer" to acidic??

[Boomer]

Also isn't the" pH 4 buffer" to acidic??

No, that is a common recommendation for pH probe manufactures

[Randy Holmes-Farley]

The reason that I picked the diluted tank water is that it is similar to tank water, but is dilute enough that there would not likely be any precipitation of CaCO3 on the tip, even slowly. In the end, I doubt it matters much what you use, within reason. :D