Does water temp affect pH?

[Dlhirst]

I took a sample of tank water to a LFS today, just to check... Nothing seems out of sorts... I just like a second opinion on my tests. The water sat in my (Michigan) car for a couple hours, so it was quite cold. LFS said the parameters were all good - except pH which was REALLY low at 7.7!

I got home and tested from the same sample, and I got the same reading - 7.7. So, I took another sample right out of the tank, and it reads 8.3, which is more like I had expected. Obviously, the biggest difference I can think of is that the tank water is 78+ degrees.

Can temperature really affect the pH like that? Or, should I be worried about something else? I change 5 gallons of my 34 gallons every weekend - so it's due... But should I be looking for something else?

[c0mp|ex]

Temperature has an affect on pH to a certain extent. Small temperature changes wont show a great amount of change but large changes in temperature will. The dissociation of pure h2o is endothermic, so an increase in temperature will actually lower the pH, the exact opposite of the phenomena that you are experiencing. I'm not sure about salt water because that is not pure water.

What you could be experiencing could be caused by a closed container and high co2 levels instead.

[Dlhirst]

Closed container makes sense, I guess. The sample was sealed tight in a pimento jar... Thanks.

[jaystampareef]

YOU must check the pH yourself at home. The pH will change in the time between leaving your house and arriving at the LFS. Trust me here... we use the best 3rd party water testing company is the business, and they WILL NOT test pH, for that exact reason. Get an electronic pH tester. best $100 you can spend on your tank.