About Dave's TF100 kit

[critterdoc]

Hiya Dave!

I'm impressed with the short delivery time and kit operation was a no brainer! I'm a happy camper with your product.

Got questions:

1. The calcium hardness test formed a noticeable amount of precipitate when I began adding reagent R-0012. If I recall accurately, the precipitate resolved by the time that blue coloration became apparent. I also had the impression that the particle size varied. I'm curious about the chemistry behind the precipitation and it's resolution.

2. About Color Change. Color changes are easily perceived in each of the drop tests, but additional drops seem to perhaps linearly increase the intensity of final color. I was not sure what to use as a visual endpoint. As an example, stage one of the CH test appears to move through an early pink to a deep red color as R-0011L drops are added and stage two moved through quite a range of blue as drops of R-0012. How do youvisually judge the colorimetric endpoints when you personally test water? Have you even done any "smackdown" testing wherein you and several others pros that you know tested the same sample at the same time using your test kit without discussing color change endpoint ahead of time?

3. Can I assume that the materials included in the blue box for "daily testing" provide an accurate enough assessment of pH to satisfy professional pool keepers?

 

[Guest]

Hiya Dave!

I'm impressed with the short delivery time and kit operation was a no brainer! I'm a happy camper with your product.

Got questions:

1. The calcium hardness test formed a noticeable amount of precipitate when I began adding reagent R-0012. If I recall accurately, the precipitate resolved by the time that blue coloration became apparent. I also had the impression that the particle size varied. I'm curious about the chemistry behind the precipitation and it's resolution.

The first reagent (R-0010) is sodium hydroxide to raise the pH and cause the magnesium to precipitate out so the EDTA titration is only testing calcium hardness and not total hardness. Swirling for about 20-30 seconds after adding the first reagent, then swirling after adding each drop of titrant will help minimize this. Also, if there are any metals present in your water there might be noticeable precipitant and and indistinct endpoint. In that case adding 6 drops of the EDTA titrant (R-0012) first before adding the R-0010 helps but remember to count those 6 drops in your final total. Finally, a magnetic stirrer REALLY helps to minimize this problem. One of our members sell an inexpensive one that works very well.
portable-magnetic-stirrer-from-apollo-pools-t1489.html

2. About Color Change. Color changes are easily perceived in each of the drop tests, but additional drops seem to perhaps linearly increase the intensity of final color. I was not sure what to use as a visual endpoint. As an example, stage one of the CH test appears to move through an early pink to a deep red color as R-0011L drops are added and stage two moved through quite a range of blue as drops of R-0012. How do youvisually judge the colorimetric endpoints when you personally test water? Have you even done any "smackdown" testing wherein you and several others pros that you know tested the same sample at the same time using your test kit without discussing color change endpoint ahead of time?

R-0011 is an indicator so the more drops you add the deeper the color becomes. Use the proper amount of drops.
As far as the endpoint to any titration test, be it CH, TA, or chlorine what you want to do is keep adding drops until there is no further color change from the last drop added and then don't count that last drop. There is no subjectiveness to this. Titration tests are not colorimetric (color matching). The only colorimetric tests are the pH test and the OTO total chlorine tests for quick daily checks. The CYA test is a turbidity test and the other tests are titrations.

3. Can I assume that the materials included in the blue box for "daily testing" provide an accurate enough assessment of pH to satisfy professional pool keepers?

Yes.

 

[duraleigh]

Critterdoc,

Waterbear has answered your questions far better than I can. He is the testing guru on the forum. He was instrumental in choosing the tests for the kit and advising me on their accuracy and usability.

The "smackdown" experiment you mention is very interesting and I don't think it's been mentioned before. Primarily, because the tests, while not perfect, are virtually always within an acceptable range for our puposes....i.e. A Calcium Hardness difference of 210 or 230 is pretty much irrelevant. We certainly need to know + or - 20ppm or so but that's about as critical as we need to be.

Likewise on the pH. 7.2 or 7.4 (usually) matters very little for our needs so that resolution is good enough. Incidentally, that pH test method is found in the cheapest kits (but with a cheaper, harder to read comparator) on up until you get very, very expensive. It's reliable, repeatable, and about the only pH methodology available for less than $100 or more if I'm not mistaken.

Last, Thank you for the kind words about delivery and instructions and thanks for your business.

 

[gtm]

Before finding this forum I had already bought a Taylor K-2006, but I recently got some replacement reagents from duraleigh. I only got these where the numbers (e.g., R-0009) were the same. The following is certainly not any kind of "smackdown" test, but I'll offer it up for what it's worth.

Before using the replacement reagents I did a side-by-side check against the remaining Taylor reagents I had. Just a habit ingrained in me from Dr. Carter's junior level Physics Lab course. I haven't tested all of them, but the ones I did test gave back exactly the same results to the level of precision of the test. For example, the TA reproduced to the 10 ppm level.

Pretty surprising, I thought, given the vagaries of drop sizes, age of the reagents, and the idiosyncracies of the tester. But the bottom line is that the results were remarkably reproducible.

 

[critterdoc]

The "smackdown" experiment you mention is very interesting and I don't think it's been mentioned before. Primarily, because the tests, while not perfect, are virtually always within an acceptable range for our puposes....i.e. A Calcium Hardness difference of 210 or 230 is pretty much irrelevant. We certainly need to know + or - 20ppm or so but that's about as critical as we need to be.

My concern was more related to variation in the observer's visual function than to the range of error of the physical tests themselves.

 

[Guest]

My concern was more related to variation in the observer's visual function than to the range of error of the physical tests themselves.

The endpoints of all the tititations are distinct enough that it should be no problem at all to determine when one more drop of titrant produces no additional color change. As I said, these are NOT colorimetric tests.

 

[gtm]

That's a good point and I worried about that, too. I thought that the pH test would likely be the most affected by visual acuity and color sensitivity, so I tested that as well. I did replicates with me (20/15, normal color vision), my wife (20/something crazy high, normal color vision), and my teenager (20/20, colorblind), and we still all managed to get the same answers. I was surprised that my colorblind son could do so well!

Since the pH test depends so much more on fine color discrimination, it seems likely that the titration tests, which depend on much more obvious changes, should be fine.

P.S. This was being typed when Evan/waterbear's response came in.