Calcium Hardness Testing

[C4ST]

Can any of you help me in regard to the "fading endpoint" issue with the TF-100 calcium hardness test? If I carefully follow the CH procedure, 8 drops of R-0012 gives me a “purplish blue” (my son called it “indigo”) color.9 drops starts to turn into a true blue, and it stabilizes at blue at 10 drops. Does a "purplish blue" or "indigo" color constitute a fading endpoint?


I have tried adding 5 drops of R-0012 first, as suggested for “fading endpoints.” If I then add 10 drops of R-0010 and then 3 drops of R-0011L, it turns pink. 3 more drops of R-0012 turns the solution purplish blue—perhaps a bit more blue than purple. Is this a fading endpoint as well?


I also tried diluting 50:50 with distilled water and adding 5 drops of R-0012 first. I then added 10 drops of R-0010, and then when I added 3 drops of R-0011L it turned blue immediately. This seems to agree with the fact that 10 drops of R-0012 gives a true blue (first paragraph of this note), and would seem to indicate a calcium hardness of 10 * 25 = 250 ppm.


I have also periodically had my water tested at pool stores, and have gotten results all over the map--from a low of 159 to a high of 280 ppm. During this same period I seem to be generating results with my TF-100 kit (aside from the "fading endpoint" issue) that are consistently in the range of 200 - 250 ppm.


Some of the variation with pool store results is probably related to different testers at Leslie Pool Stores using different amounts of carefulness in the testing procedure. However, during this time I have had two tests done at Anthony & Sylvan, and they use the LaMotte WaterLink Spin tester, which would seem to remove the human factor from the test results. A&S has generated results of 159 ppm and 178 ppm--both of which are low for a plaster pool, and this concerns me.


Are any of you familiar with the LaMotte WaterLink Spin tester, and the quality of results that it generates?


Thank you in advance to any of you who are able to provide some insight to my question.

Carl

 

[jblizzle]

You just add drops until the color change stops.
Sounds like 10 drops is blue, you should add an 11th drop to confirm no further change and then your final count is 10.
Does not sound like you are getting a fading end point.

Ignore pool store testing ... we don't trust it for the very reasons you stated ... unreliable and not consistent.

Stick with the Taylor test kit.

 

[Richard320]

I pass through the indigo stage too. Sometimes an extra cycle of the speedstir will push it to blue, sometimes not. But keep going until you get to sky blue.

 

[Spa Owner]

Some of the variation with pool store results is probably related to different testers at Leslie Pool Stores using different amounts of carefulness in the testing procedure. However, during this time I have had two tests done at Anthony & Sylvan, and they use the LaMotte WaterLink Spin tester, which would seem to remove the human factor from the test results. A&S has generated results of 159 ppm and 178 ppm--both of which are low for a plaster pool, and this concerns me.


Are any of you familiar with the LaMotte WaterLink Spin tester, and the quality of results that it generates?

To answer this specific question...

The spin tester does not use methods of analysis conforming to the standard methods for examination of water and waste water. This is the lab standard for water testing and most other test kits use a standard method.

In field testing we found inconsistent results even on same sample prepared identically in the same way. Of specific concern the CH,TA, pH and FAC were all inconsistent with variations into the 80 mg/l range on same samples the CYN was okay and repeatable.

The spin tester is sold o shops on the basis it is faster to get a test done. We don't think it is. Using a photometer and following standard procedure we can complete a water test and record results before the spin is done.