Purple ph test sample.

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
Allen G Myerson

Purple ph test sample.

Postby Allen G Myerson » Sat 07 Jan, 2012 23:24

If you are using a Taylor K-2005 or K-2006 test kit, then 30 drops of reagent R-0005 (acid demand) would indicate an alkalinity of at least 190 ppm.


Allen G Myerson

Purple ph test sample.

Postby Allen G Myerson » Sun 08 Jan, 2012 10:45

Here is something you can do.

First, do the total alkalinity and acid demand tests as normal. Then redo both tests, but switch the TA and acid demand titrating reagents and compare the results. (The titrating reagents are the reagents that you add while counting the number of drops)

For example, if it takes 10 drops of the TA titrating reagent to do the TA test and it takes 16 acid demand drops to do the same TA test, then that would mean that 1 drop of the TA reagent would be equal to about 1.6 drops of acid demand reagent.

Be sure to swirl well between drops to ensure thorough mixing.

I suspect that the high pH is most likely due to new plaster.
chem geek
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Purple ph test sample.

Postby chem geek » Sun 08 Jan, 2012 21:09

Allen G Myerson wrote:I suspect that the high pH is most likely due to new plaster.

I agree. When I plugged in the numbers, a high TA alone doesn't explain the huge acid demand.

One drop in the acid demand test represents 9.16 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in 10,000 gallons. 30 drops is equivalent to 34 cups of acid in 10,000 gallons. Let's assume your pool is larger than most at 20,000 gallons. Then at a TA of 200 ppm, the pH could be 9.5 since after the acid it would get down to close to around 7.5 (the TA would drop by 54 ppm to 146 ppm). Or if the TA is 300 ppm, then the pH could be 9.2. Even at 300 ppm TA, the pH would not rise above 8.9 so Allen is most likely correct in figuring out that your pool may be newly re-plastered and that the pH rise is from the plaster curing. If some of the pH rise, say to 8.0, was from carbon dioxide outgassing, then if the rest to 9.5 was from plaster curing then it would increase the TA by 60 ppm to 260 ppm and would add 10 pounds of calcium carbonate to the water.
Allen G Myerson

Purple ph test sample.

Postby Allen G Myerson » Sun 08 Jan, 2012 21:36

The poster is reporting a TA of 90 ppm. 30 drops of acid demand to get in the readable pH range would be equivalent to an alkalinity drop of about 108 ppm. And, then you would still have to go down from there to a pH of 4.5. Therefore, a TA of about 90 ppm and an acid demand of about 30 drops might be possible, but I think that it would be unlikely.

I think that the water would have to start out with very little carbonate alkalinity and a hydroxide base would need to be added. This could be consistent if a freshly plastered pool was filled with very low alkalinity water.

With almost no alkalinity, the pH would rise much faster and higher due to the calcium hydroxide (the pH is probably well over 10).

And then, most of the TA would be gone when the pH was lowered back to the 7 to 8 pH range.

What is the TA of the fill water?
Jignesh
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Re: Purple ph test sample.

Postby Jignesh » Mon 10 Dec, 2018 03:55

A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH (acidity or basicity) of the solution can be determined visually. Normally, the indicator causes the color of the solution to change depending on the pH.
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Re: Purple ph test sample.

Postby Teapot » Tue 11 Dec, 2018 09:27

Jignesh wrote:A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH (acidity or basicity) of the solution can be determined visually. Normally, the indicator causes the color of the solution to change depending on the pH.

No sh!t Sherlock
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Re: Purple ph test sample.

Postby dynamictiger » Mon 17 Dec, 2018 00:47

A true purple blue can form in the presence of extreme high bromine. The bromine combines with the phenol red to form bromo-phenol blue. Someone with less experience may mistake this for extreme high pH, when in fact the opposite is the case. Be wary of this trap.

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