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.
chem geek
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Purple ph test sample.

Postby chem geek » Sat 16 Jul, 2011 13:55

Dechlorinating through an activated carbon filter will lower the pH since chlorine usage/consumption is acidic so that doesn't necessarily tell you the pH at the time the chlorine is high. Since pool water is buffered, you can dilute the water with distilled or deionized (unbuffered) water since that has a negligible effect on the pH. Just make sure the water you use for dilution is truly unbuffered -- it's TA should be 0 and pH near 7.0 (though that is actually less important if the TA is near 0).


Guest

Purple ph test sample.

Postby Guest » Thu 05 Jan, 2012 22:38

I'm in a similar predicament. However my chlorine levels are low (on purpose as we have a solid pool cover which blocks out sinlight) but my ph level is sky high (rich purple). Two litres of acid later and still no change. Yet water is squeaky clean and clear. Alkalinity is around 90ppm which is spot on a concrete pool. Anyone able to help?
chem geek
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Purple ph test sample.

Postby chem geek » Thu 05 Jan, 2012 22:58

If you are using a good Taylor test kit (such as the K-2006 or even the K-2005), then use the acid demand test to see how much acid would be needed to get the pH lower. You could also get some new pH reagent, just in case it went bad.
Guest

Purple ph test sample.

Postby Guest » Fri 06 Jan, 2012 04:05

Many thanks for that. When I did the acid demand test the colour of the solution went from purple to yellowish after about 30 drops and it bypassed the pink phases altogether. I took a water sample to the pool shop and they also came to the same conclusion...ph is too high. Feels like I am going around in circles. We are in an area where the water is high in alkaline and perhaps that is the problem to begin with. Considering the water looks terrific and smells ok, is there a health risk to swimming in a high ph pool other than burning eyes? Many thanks for your assistance. Cheers
Alex
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Purple ph test sample.

Postby chem geek » Sat 07 Jan, 2012 03:01

Water that is high in Total Alkalinity (TA) will tend to rise in pH, but it will usually stop rising at around 8.2 to 8.4. However, a high TA will take more acid to lower the pH. So that does sound like what is happening and unfortunately it will just take a lot of acid to get your pH lower. Add it slowly over a return flow in the deep end with the pump running and when you are done lightly brush the side and bottom of the pool where you've added the acid to ensure thorough mixing. You do not want it pooling at the bottom of the pool (it's denser than water until it gets thoroughly mixed).
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.
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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?

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