Water temps 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?

[MUCHO REEF]

Wow, great question, just found this and surprised it has sat for a week untouched with 60 views.


I can't honestly say that I know for sure, but off the top of my head I would yes, slightly to marginally, yes, for the reasons listed below. When I don't know for sure, I will pull out one of my books or hit the net and this is what I found.


A direct quote,


The reason temperature affects water's pH is that water molecules tend to break down into their constituents, hydrogen and oxygen, as the temperature increases. As temperatures increase, a larger proportion of water molecules break up, producing more hydrogen, which then increases the pH of the water

Read more: The Effects of Temperature on the pH of Water | eHow.com http://www.ehow.com/about_6837207_ef...#ixzz1CLpAGiFC


But this speaks of fresh water, so I continued to read.


Another quote


•Temperature will have a measurable yet very slight effect on the pH of water. In fact, pure water has a pH of exactly 7 only at 25 degrees Celsius, or 77 degrees Fahrenheit. As the water temperature goes up, pH goes down. The converse is also true, in that colder water has a higher pH value. At 60 degrees Celsius (140 degrees Fahrenheit), pure water will register a pH value of 6.96. In other words, the change is very slight and cannot be registered with crude measurement techniques such as pH test strips.


Read more: The Effects of Temperature on the pH of Water | eHow.com http://www.ehow.com/about_6837207_ef...#ixzz1CLpAGiFC


Again, this speaks of fresh water. I defer to the pros, can anyone assist this reefer with an answer? Jim, what do you think?

Mucho Reef

[rmalone]

The amount of time that the water sits out will have an effect on the ph though 2hrs shouldn't have made much difference. If it was tested with a non temp compensating meter and the temp of the sample was real low it would skew the ph value also.

[dlhirst]

That could have been the story. It was sealed up in a pimento jar and left in a car. So, temp was likely well down into the 40s or 50s... I currently test with a API test kit - drops. So, there is no "temp compensation" there. But, I do not know what the LFS used to test. I am looking to buy a digital meter, I think I have another thread here about that.

[Wy Renegade]

But if the effect was being caused by the temperature, should the pH have gone up rather than down? According to the quotes and links, increasing temp. causes pH to drop while decreasing temp. causes pH to rise. I assume it is cold in Michigan right now so the temperature of the sample went down rather than up, correct?

[MUCHO REEF]

Good point. Also, the link spoke of fresh water, not salt.