[felis]

pH probes are very temperature dependent so you will need to also have a temperature input that is accurate to .1 F.

It would depend on the accuracy you'd like to achieve. There is a table on my Milwaukee 7.01 calibration solution which shows dependency in question; within the range from freezing to boiling water the numbers are 6.98 to 7.14, which translates to +-2ppm CO2 error using popular KH/PH formula for KH4. Again, this error is for 0-95degC range; if we look at the same table in normal aquarium 20-40degC range, the difference in pH would be 6.98-7.04 which brings CO2 error to sub-ppm making it insignificant.