R0004 result not equal to R0014

[jontomosicz]

I have both Taylor ph test kits, the 44ml block used with R0004, and the small block used with R0014 reagent. I've noticed that I get different readings with each kit. The R0004 usually measures 0.2 higher than the R0014, sometimes more. In the pH test, 0.2 is a big difference. I realize there's a margin of error with these tests, but due to the consistency of these results I don't think that's what I'm seeing.

My reagents are about 6 months old and not expired yet. I even purchased a second bottle of each reagent thinking one of them must be bad, but I get the same results with the new reagents.

Has anyone else experienced this?

Here's a picture I took this morning from my tests. To my eyes (and my wife's) the 44ml/R0004 test is right at 7.8. The small/R0014 block is more like 7.6...it still has a peach tint to it, definitely not 7.8.

 

[YippeeSkippy]

I personally would not worry about such minute differences and instead pick one or the other to use.

Make sure you are filling the test block to the line, and that the bottom of your meniscus curve is at the line, not the top.

Maddie

 

[domct203]

As mentioned, this is not a big discrepancy, especially with such a subjective (color matching) test. For all you know, the actual pH could be 7.7, which would give a .1 deviation to each testing method, pretty darn good for visual color matching outside of a controlled light source environment.

 

[Poolzzz]

Although you error isn't that big a deal, since you are seeing a bias and not a random error then it might be worth tracking down the reason. Filling the tubes precisely and correctly is an obvious source of bias. Also maybe try one more or one less drop in the smaller vial to see if you eyes are being fooled by the saturation levels rather than the actual color. Another cause could be your source light, if the light has an uneven spectrum (most flourescent or led) it can bias the colors -- try viewing against a cloudy sky background. I suppose it could also be the test blocks themselves, I'm not sure the tolerance Taylor has on the standards on their blocks. By the way, your pictures aren't coming through for me.

 

[wayner]

Does the actual size of the sample really matter for the pH test? Doesn't this test measure the tint of the redness?

Here is my experience - If you are yellow then pH is really low. Orange and it is kind of low. Red is perfect. Pink is getting too high. Pinky purple means you are way too high.

Adding more drops or changing sample sizes isn't going to change an orange sample to pink, is it?

And isn't it possible that the colour on one of the vials for the 7.2, 7.4, etc colours may be fading. I know that on toys that red dyes seem extremely susceptible to fading from UV exposure - perhaps the same is happening to the red on the test vials.

 

[jontomosicz]

I try to measure the sample size out to the line, but from what I've read throughout this forum the sample size is not critical for the pH test. Unless I'm way off in my measurements, the color should be the same.
I have tried one or two less drops of reagent, but it doesn't make a difference in the color. Just makes the color more or less intense.

0.2 may not be a huge difference, but it seems significant. My pool's pH will stay at 7.8 for days...if I'm measuring with R-0014. So the pH is good and no need to add muriatic acid. However, If I measure the same water with R-0004 (and the bigger test block), it measures 8.0. So I need to add acid. That's where I'm concerned...which test is accurate?

 

[JoyfulNoise]

However, If I measure the same water with R-0014 (and the bigger test block), it measures 8.0. So I need to add acid. That's where I'm concerned...which test is accurate?

R-0014 can ONLY be used with the midget comparator. R-0004 can ONLY be used with the larger #9056 comparator block. The R-0014 is less concentrated than the R-0004 and will not give the proper color match when used with the larger comparator block.

 

[jontomosicz]

Good thought regarding worn out colors on the test blocks, but both of mine are only a year old. They're never left out in the sun. So I don't think that's it.
Not sure why the pictures didn't come through, but I'll try again...

 

[duraleigh]

Good pic. I don't see the difference that you do. I would call them both very close to 7.6 and be done with it.

 

[jontomosicz]

Mixed up my reagent numbers...I'm using the correct test blocks.

 

[JoyfulNoise]

Good thought regarding worn out colors on the test blocks, but both of mine are only a year old. They're never left out in the sun. So I don't think that's it.
Not sure why the pictures didn't come through, but I'll try again...
View attachment 70205

It would be easier to make out the cooors if you could put a white background (try printer paper or a paper plate) behind both. Sitting in the window sill is not helpful.

That said, they both look about 7.7-7.8 to me. The midget block only has color patches for 7.5 & 7.8. So it’s harder to compare that to the 9056 block. But, based on your picture, I’d call it 7.7-7.8. That’s “good enough” for pools....if you want a more precise number, then get a digital pH pen meter. Miron-L are the best ones I’ve worked with.