pH Tests Differing

[CaliTiger09]

I am getting a large difference in my ph tests. My comparator block with the phenol red shows 7.5 and my ph meter reads 7.9. I took some to the local pool store today to just get another test to compare and they got 7.9. They also had two other test results that differed from mine significantly. But they also had reagents just sitting opened on the counter so I’m not sure if that would impact a test or whether it means I can or can't trust them. My ph meter also reads correctly when calibrated in a 7.2 solution.

Any thoughts or has anyone experienced this before?

 

[ajw22]

Segal's law - Wikipedia

en.m.wikipedia.org

Any pH in the 7s is fine. Both tests say your pool is ok.

 

[CaliTiger09]

Segal's law - Wikipedia

en.m.wikipedia.org

Any pH in the 7s is fine. Both tests say your pool is ok.

There’s a number of those values that don’t work for my LSI calculations that I am aiming for, however.

 

[proavia]

There’s a number of those values that don’t work for my LSI calculations that I am aiming for, however.

Use PoolMath, which computes CSI.
CSI is a better indicator for pools then LSI, which is used for boilers.

Believe the comparator block in your TF-Pro.
If having difficulty with thereading, try using 4 drops of pH reagent instead of 5. This sometimes helps in comparing the color.

 

[ajw22]

There’s a number of those values that don’t work for my LSI calculations that I am aiming for, however.

Read CSI and LSI - Further Reading