pH in the KH director measurement cell

[KGV]

Does anyone know why the pH in the measurement cell of the KH director never reaches the pH of the tank when starting an alk test? My tank pH is typically 8.3, but the highest pH in the measurement cell at the start of the titration is 7.8.
Both the tank pH probe and the KH director pH probe are calibrated and show similar results.

 

[jsker]

@Billldg

 

[Billldg]

I can not give you a scientific answer, but, I have thought about this, and you have to remember, the PH probe in your KHD is just sitting there not doing nothing between test and is not influenced, while your tank PH probe is constantly reacting to your tank which is constantly changing. The only time your PH probe in your KHD sees actual tank water is when you do a test, otherwise the water just sits their evaporating. As of right now mine is at 4.77 while my tank is at 8.27. Any water in the KHD will be a room temp while the PH probe in the tank is 4 degrees higher.

@Ditto @Vinny@GHLUSA , am I wrong in this assumption, is so please correct me.

 

[Ditto]

I would think it is not in their long enough to get to the tank PH level because it fills the chamber and immediately starts the test.

 

[KGV]

I would think it is not in their long enough to get to the tank PH level because it fills the chamber and immediately starts the test.

Yes, I think this plays a big role and reduces the measurement time a lot while not affecting the outcome.

I have never opened the measurement cell and I was worried that there is a substantial amount of acidic fluid remaining between tests that doesn't get drained.

 

[ck24]

The water doesn’t sit in the cell very long to give you the right PH value. Once it fills the cell completely it starts adding reagent.