Learning to read PH.

[AUSpool]

Another trick to seeing change in the phenol red pH colors is to use the acid and base demand reagents dropwise and see the color change.

 

[Woody007]

There are plenty of threads discussing electronic meters, mostly handhelds. Electronic testers need calibration to two points and storage in a potassium chloride solution both of which costs money and takes time and even then the results can be skeptical. Old meters, poor calibration, cheep calibration fluids, incorrect storage, old probe, old batteries, etc. will all lead to poor results. People often confuse extra decimal places with accuracy. Without calibration an electronic meter is nothing more then a random number generator. And at the same time 4-5 drops in a pH comparator is more than accurate enough for most users.

Just like anything, you have to take care of it to work correctly.
I would trust a digital meter anytime over a colorimetric guestimate, especially my eye.
The founder of our company invented the pH meter, and I think he might agree as well. (if he were still alive)

 

[Buggs]

Another trick to seeing change in the phenol red pH colors is to use the acid and base demand reagents dropwise and see the color change.

You have intrigued me with this comment. Could I trouble you to elaborate or point me to where I might learn how to do this?

 

[AUSpool]

Just like anything, you have to take care of it to work correctly.

And that is their achilles heel. The average person has no idea how to how to use one correctly or take care of it. They just don’t know that their $30 meter requires $100+ in calibration and storage solutions. They buy a cheepy off the net, don’t calibrate it, don’t rinse it, and probably just leave it out in the weather at their equipment pad and because it’s still giving a readout to two decimal places they think it’s working fine. Even if the instructions include directions for the proper care and use most wouldn’t read it.

 

[AUSpool]

You have intrigued me with this comment. Could I trouble you to elaborate or point me to where I might learn how to do this?

Unfortunately I’ve just realized that this is really only for those with the Taylor K2006 kit. It has a larger volume pH comparator and comes with acid and base demand reagents (R0005 and R0006). In the old days, prior to PoolMath, we would use acid demand to workout how much acid to add. We would add the R0005 drop wise to the treated pH sample in the comparator until the color matched our desired pH. Then from a table the number of drops can be used to calculate the volume of acid required. It slowly changes the color from >8 down to 7.0 so you can see the entire range. The acid and base demand reagents are specifically formulated for the Taylor comparator and wouldn’t work in the TFTestkits comparator. Sorry for getting your hopes up.

 

[Buggs]

Hi Steve, Your effort was not for naught. I now understand that you were referring to the residual chlorine test. I’ve used that test in the past with my previous test kits, though I routinely skip it in my water testing. It had slipped my mind, so I didn’t recognize it with your initial comment. I now see how it might be used to more precisely determine the sample pH. Thank you for clarifying.

I was interested because for many years I have conducted my pH tests with no issues using a Guardex kit from 1999. I also have a 2012 Taylor kit but preferred the Guardex comparator block. That testing procedure came to an end this summer because my Guardex reagent became depleted and I learned that Guardex has terminated manufacturing their reagents, so I can’t get any fresh stuff. Since receiving my new TF-Pro test kit, like the OP, I struggled with their pH color matching. I recognize that a precise pH value is not needed for pool management, but was slightly frustrated by the increased difficulty.

My pool pH likes to sit in the high 7’s. I’ve noticed that after preparing a TF-Pro pH sample, the hue of the sample color in this range matches the hue of both the Guardex and Taylor color blocks. They only differ by their color saturation. Whereas the TF-Pro color block also has a slightly different hue, so both hue and saturation must be considered in determining the pH value. (e.g., “No purple in the sample”)

Curiosity prompted me to purchase a decent pH meter. Using that as a benchmark, I’ve found that I can best visually estimate the pH by preparing the TF-Pro pH sample, but gauging it with the Guardex comparator. However, there is an offset: My visual pH estimation is consistently 0.1 lower than the pH value I measure with the meter. In the sample shown below, the meter measured a pH of 7.88.



Yes, this is esoteric. If you are happy with your current pH testing, I suggest you don’t go down this rabbit hole.

There’s a pertinent proverb that says, “A man with one watch knows what time it is. A man with two watches is never sure.”

 

[AUSpool]

Hi Steve, Your effort was not for naught. I now understand that you were referring to the residual chlorine test. I’ve used that test in the past with my previous test kits, though I routinely skip it in my water testing. It had slipped my mind, so I didn’t recognize it with your initial comment. I now see how it might be used to more precisely determine the sample pH. Thank you for clarifying.

Residual chlorine would be a DPD, FAS/DPD or OTO where manipulation of color would require adding bleach but in this case the color is directly related to the concentration of FC rather than pH. I was referring to the acid and base demand extensions of the pH test as found in some of the Taylor kits like the K2006.

 

[Buggs]

Hi Steve, You are correct that I was incorrect. I actually understood your message, but I mis-spoke (mis-typed?) when I wrote "residual chlorine", when we were talking about pH. I should have looked up my Guardex test to refresh my memory:



Thx for keeping me honest and the message on track.