Strange pH test

[PoolDoc]

I ran out of the Taylor Phenol Red reagent (R-0014) tonight so I broke out a new bottle. When I tested the pH with that I got a color that didn't match anything on the color comparator; it was a much lighter pink. It's clearly pink but light like the orangey/yellowy colors at the lower end of the pH scale. I ran the test a couple more times with identical results

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The reagent was purchased this past spring as part of a refill kit from Ben.

Is this just a bad bottle of test reagent?

Hi All;

I'd like to throw my 2 cents in here, too:

Both R-0004 and R-0014 are Taylor's blend of phenol red, a pH buffer, and some sodium thiosulfate (to allow the phenol red to continue working when the chlorine level is above 3 ppm!). The ONLY difference between the two, is that R-0004 is slightly more concentrated than the R-0014, to compensate for the larger sample size used in the comparator from the K2005/6 kits, rather than the smaller sample from the comparator in my PS200 (relabeled K1000 -- I don't like their instructions!).

In a reversal of the case with DPD colorimetric testing, phenol red colorimetric testing is based on changes in hue, rather than saturation. That is to say, pH is judged by whether the solution to which phenol red is added is orange or yellow, and NOT whether the orange is intense or saturated. This is the opposite of DPD colorimetric (also opposed to titrimetric testing such as the FAS-DPD test, which looks for disappearance or a radical shift of color). DPD colorimetric testing is based on how red the sample is, and not which red is displayed.

For this reason, both R-0014 and R-0004 will give similar results, used in either comparator. However, the colors displayed will be less intense (R0014 in a K2005 comparator) or more intense (R0004 in a K1000 comparator) than expected.

I've only experimented with this a little, but it appears to me that the apparent error, from using the 'wrong' phenol red reagent would typically be one color bar or less. This would be true whether the 'wrong' reagent is R0004 or phenol red from some Walmart or Kmart kit. (Of course, to the best of my knowledge, none of the other kit manufacturers have added the sodium thiosulfate / buffer mixture, to all phenol red to be used above 5 ppm chlorine.)

But pink . . . is NOT a color that would normally EVER be produced by a phenol red solution, regardless of pH, and regardless of whether R-0004 or R-0014 is used. The only pink I know of, with any of the chemicals in the kits added alone, would be DPD in chlorinated water.

Since the R0014 is NOT a reagent we fill, I can think of only a couple of possibilities:

• Somehow, we sent you an old bottle of R0002 DPD solution that had gotten mixed in with the R0014. I would have said this was impossible, since we haven't kept any of that around for several years, but after all the problems I'm having this season, finding out that we'd made yet another 'impossible' error wouldn't surprise me.
• Alternatively, you got a bottle of Taylor R0014 that was misfilled. Taylor has (as have we) misfilled or mislabeled bottles before. This is the scarier alternative, since if true, it's unlikely we got only ONE bottle of bad stuff.

Either way, if you'll email me with your name / address, etc. and reference this thread, I'll try to send out some known good R0014 to you this week.

Regarding reputation . . . I need to see what's going on. Unfortunately, the only way I can do this (even with administrative powers) is to "seize" your accounts (GHM and fcfrey) and then log in, and take a look. This is a serious issue, either way, so I hope you'll forgive me for taking over your accounts briefly. You'll get a new password request, requiring you to sign and create a new password after I finish. Once that's done, you can go into your profile and restore your password to it's original state. (I can't do this, since passwords are stored in an encrypted form that I can see, but can't decode -- so I have no way of knowing what your password was.)

Sincerely,

Ben
"PoolDoc"