Can you please explain your temperature statement Randy. Does the pH probe measure the temperature?
No it doesn't, but pH measurement is somewhat temperature sensitive and controllers usually have a separate temperature sensor that they may be using to determine the pH calibration and measurement adjustments.
Aquarium Chemistry: Measuring pH with a Meter ? Advanced Aquarist | Aquarist Magazine and Blog
http://www.advancedaquarist.com/2004/2/chemistry
A Comparison of pH Calibration Buffers by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2005-02/rhf/index.htm
from the first one:
Temperature Effects on pH Measurement
There are two different ways that temperature impacts pH measurement. The first involves actual chemical changes in the solution that you are measuring. Acids can, for example, become stronger or weaker as the temperature is changed. This is how calibration standards change their pH as a function of temperature (which is discussed in more detail in the calibration section below). If the solution has solids in contact with it (as is the case with saturated limewater in the presence of excess solids), the temperature can also impact how much acid or base is in solution impacting pH, and how much is just solid sitting on the bottom of the container. These effects are specific for every solution that you will encounter, and there is nothing general that one can or should do about this, except be aware that it happens.
The second impact of temperature is on the pH electrode itself. pH electrodes change their response in a very clear way as temperature is changes. They respond more strongly to pH changes at higher temperature than at lower ones. At 100 ºC, they change their output potential by 74 mV/pH unit, and at 0 ºC, they change by 54 mv/pH unit. Because pH meters are typically standardized at pH 7 (that is, zero mv = pH 7), the error from temperature differences gets greater and greater as the pH being measured gets further from 7. So it may be trivial when measuring something with a pH of 7.1, but very important when measuring something with a pH of 10 (or when calibrating with a pH 10 buffer).
There are usually three different ways of taking temperature into account. One is to make measurements close to the temperature at which you calibrated the meter (say, within a few degrees). The second is to "tell' the meter what the temperature is (digitally or with a dial). The third is that some meters have a temperature probe, usually called an ATC, which you stick into the measuring solution. This probe reports the temperature back to the meter, and the meter makes any necessary corrections (for this type of temperature effect).
As long as you use one of these three ways of dealing with temperature issues, you will get reasonably accurate readings.
