pH calibration with peristaltic pump and ph sensor issue.

[paokaras31]

Hello guys.
Just giving a little heads up to everybody who use an automated pH calibration system.
Mine is an astral pool Ph Basic 5l/h. It has a pH sensor after the main pump and filter and a muriatic acid 32% inlet before the swg cell .(swg cell is the last in line on my main feed line to the pool) Just to be clear my setup is ool main return-main pump-main filter-ph sensor-muriatic acid inlet-swg cell-pool)
I have noticed that my TA was drifting low (40 to even 30) needing a lot of baking soda to correct. I had the pH set to 7.8 on the astral ph pump. I then checked the ph with a classic taylor kit and it was between 6.8 an 7.2 (can never be exact with these color tests!!) I doubled checked with another pH kit from a neighbor. I then recalibrated the pH sensor but it still showed 7.8. I bought a new pH sensor to be 100% sure: still 7.8.
I then took a bucket of pool water and removed the sensor from the piping and used it in the bucket........7.2 !!!!!!
So all this time I have been calibrating a 7.2 pH thinking I was on 7.8. That explains my low TA as well.
Anyway I now have the pH pump set at 8.4 and I am geting an actual pH of 7.8 (which is what I need to have balanced water as per pool math calculator).
It seems that turbulence in the pipes increases the pH topically ( ?) and the sensor reads high....Anyway ,I just thought I shared my experience and warn anyone with a pH sensor to doublecheck their readings.
Cheers

 

[dschlic1]

Do you have the sensor mounted directly in the main discharge pipe? If so you are probably exceeding the liquid velocity of the sensor. Most sensors need to be on a separate sample line where the flow rate through the flow cell can be controlled.

 

[paokaras31]

Hi
It is on the main discharge pipe . I think the velocity is roughly the same before and after the filter and I cannot put it between the pump and the filter due to spacing issues (my engine room is below ground and piping is angled) . Her is the installation instructions:

 

[jonpcar]

Just giving a little heads up to everybody who use an automated pH calibration system.

....Anyway ,I just thought I shared my experience and warn anyone with a pH sensor to doublecheck their readings.
Cheers

@paokaras31 ...that is really nice to know for those of us considering a pH control system. Thanks for the heads-up! With the calibration “adjustment”, are things working out?

 

[VinceL]

I have the Hayward Sense and Dispense system that monitors pH and ORP. The probes are inserted in a small chamber that has an input and output. The input and output use a small diameter tube. Water is fed into the chamber from just before the pump intake and is fed back into the water flow after the SWG. There is third tap off the chamber which is where I take water samples for testing. The flow rate when I open the valve is pretty low. My test results with the water samples is never more than .1 from the pH reported by the pH probe. Each spring after I install the probes from being stored inside during the winter, I do have to check them against actual sample testing. Some springs I have to recalibrate the pH probe. The most I ever have to calibrate it is .2.