Measuring PH accurately

[ccronje]

Hi All,

I'm struggling to accurately determine the PH of my water and I was wondering if anyone can explain why I get such different PH readings when testing with strips vs the API PH test kit I have.

According to the JBL test strips I have the PH is around 6.5 or not even registering (see attached example) and another test strip I have (Voonline) shows the same. However, when I test with a proper PH drop test like the API PH test, PH measures much higher at around 7.0.

Is this big a different to be expected, or is there something else going on?

Thanks
Chris

 

[Aiken Drum]

A liquid test is generally more accurate than a test strip. In both cases these are home test kits though, not laboratory testing.

 

[Colin_T]

Bromothymol Blue is the most common reagent used in a liquid pH tester and that is more accurate than paper test strips. The pH of the water in the phial looks close to 7.0. If you want more accurate, get a digital pH meter and some calibration solutions.

 

[Andy Sager]

The issue with test strips is that unless the strips are stored properly, they can become highly inaccurate. This is why most do not recommend them. Using liquid tests with Bromothymol blue or Phenol Red as the test reagent are usually more accurate but as Aiken and Colin said, these tests are not going to be 100% accurate to the number but a close enough answer for our purposes.