Difference in pH Testing Kit Readings?

[lances4803]

I used the pH test kit that came with my TF-100 and get a reading of 7.2.
I thought this was very low considering the pool company tested the water at 7.8.
I then used the Pentair test kit that came with the pool and it tested at 7.6.
(All tests have been conducted a couple of times with the same results.)

What could cause the difference between the TF-100 and the Pentair kits? I am inclined the believe the Pentair as it is closest to the pool company

 

[JasonLion]

The PH testing reagent can go bad if it is several years old, or has been exposed to extreme temperatures. The PH test results can also be wrong if the FC level is fairly high. The PH test in the TF-100 is reliable up to an FC of 10, and fairly close up to an FC of 15. Some of the other brands start being off at lower FC levels. Other than those two possibilities, the PH test in the TF-100 is almost never wrong. The PH test in the Pentair kit is based on the same color indicator and is fairly good, but it starts being off at somewhat lower FC levels than the one in the TF-100.

 

[AnnaK]

The PH test in the Pentair kit is based on the same color indicator and is fairly good, but it starts being off at somewhat lower FC levels than the one in the TF-100.

I'm not sure I understand this. If the Pentair uses the same indicator as the TF100 (phenol red at the same concentration, presumably) then why would it be off at lower FC levels?

 

[Richard320]

I used the pH test kit that came with my TF-100 and get a reading of 7.2.
I thought this was very low considering the pool company tested the water at 7.8.
I then used the Pentair test kit that came with the pool and it tested at 7.6.
(All tests have been conducted a couple of times with the same results.)

What could cause the difference between the TF-100 and the Pentair kits? I am inclined the believe the Pentair as it is closest to the pool company

The color samples can fade with age, especially if you leave it out in the sun.
What happens if you cross reagents with the test kits?

 

[JohnT]

I'm not sure I understand this. If the Pentair uses the same indicator as the TF100 (phenol red at the same concentration, presumably) then why would it be off at lower FC levels?

Taylor adds chlorine netralizer to their phenol red. That means the Taylor kit doesn't have problems with chlorine until the chlorine is at a higher level than the Pentair kit.

 

[AnnaK]

Thanks John.

 

[chem geek]

Taylor adds chlorine netralizer to their phenol red. That means the Taylor kit doesn't have problems with chlorine until the chlorine is at a higher level than the Pentair kit.

And this isn't as easy as it sounds. If you were to just add sodium thiosulfate chlorine neutralizer as in the R-0007 reagent in the TA test, the neutralizer itself and the neutralization process can result in a change in pH with excessive use usually resulting in a higher pH. So Taylor is very careful to use a combination of proprietary neutralizers to not substantially affect the pH up to reasonable FC levels of at least 10 ppm. It's this kind of care and attention to detail and accuracy that has us promote Taylor and Taylor-based kits (such as the TF-100).

 

[Hurricane Gio]

I'm not sure I understand this. If the Pentair uses the same indicator as the TF100 (phenol red at the same concentration, presumably) then why would it be off at lower FC levels?

Taylor adds chlorine neutralizer to their phenol red. That means the Taylor kit doesn't have problems with chlorine until the chlorine is at a higher level than the Pentair kit.

I just about a TF-100 kit and figured I should use up the generic test kit regents that came with my pool in February. Or should I use the Taylor ones now?

Thanks!

 

[AnnaK]

Oh, go ahead! Splurge! Use your new test kit. You know you want to.