Vital Sine PH Monitor temperature innaccurate?

[lcdrbrentcarrol]

Hi folks!
Sorry, but I am reposting this from the equipment forum as suggested by another member...



I have a vital sine pH monitor and it reads about 3 degrees above what my other 4 thermometers in my system read (even one that is directly beside it). Now, I know there is a strong correlation between pH and temperature and am a bit miffed that I can't find a single resource to fix this one.

Tank temp (on 4 other thermometers): 79
Temp read by this vital sine: 82.5

It's reading a pH of 8.12 (average), so with a negative temperature correction I think it should be reading roughly 8.3.

Any thoughts?

And if you could (because my life tears me away from my aquarium more than I'd like) please respond here for the masses and to my account at brent.carroll@navy.mil.

Thanks!

[Randy Holmes-Farley]

The pH correction with temperature is not that large. 3 deg F makes very little difference in pH at pH 8.1, assuming that you calibrated at pH 7 and 10.
Not even enough to bother worrying about. I believe that the effect is less than 0.01 pH unit for a 3 deg change at pH 8.1. :)

[lcdrbrentcarrol]

Thanks! I followed the advice in the equipment forum and re-calibrated at tank temperature.

I am now reading 81.6 degrees at 8.17 pH (1 degree = .05 pH). So lesson learned here is that vital sine also calibrates to temperature... duh!

Again thanks!

[Randy Holmes-Farley]

Maybe.

Bear in mind, however, that the pH of standard calibration buffers can vary substantially with temperature. Especially pH 10. That is a different effect than the meter correction itself. The chemistry of the buffers actually changes. FWIW, 1 deg F = 0.05 pH correction is way too large. Both in the well established theory and on my pH meter, a 10 deg C (18 deg F) correction makes only about a 0.04 pH unit change at pH 8.3. The correction is even smaller at pH 8.1.