chlorine levels and pH reading

[rlsnights]

I know that high chlorine levels cause the pH reading to be inaccurate.

Can anyone tell me how high the chlorine is when this starts to happen?

Thanks,

Patricia

17K inground white plaster, hayward pump and filter system jet vac sweep

TC 8
pH 7.5
TA 120
CH 260
CYA 45

 

[anonapersona]

Above FC = 10 pH readings are not to be acted upon.

Ok to trust pH below FC = 10

 

[JasonLion]

To add to what anonapersona said, there is actually some slight error even when FC is below 10, but it isn't considered significant. The error increases as FC continues to rise, until FC gets into the low 20s, and then the PH reading suddenly becomes very dramatically wrong.

 

[rlsnights]

Thanks. Without really knowing it I have been doing approximately what is implied here - not trusting the pH reading above 8 - 10 ppm.