Need to understand TA vs pH!

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

Need to understand TA vs pH!

Postby cretanrunner » Sun 09 Jun, 2013 11:05

I've read various posts around this subject, but am still confused, so I'm hoping someone will explain so that I can understand the theory here.

My pool pH tends to rise all the time. I add acid, which brings it down to 7.2 - 7.3, but within a week it is heading off upwards again.

Here in Crete, no-one has heard of TA and I have only just managed to source a test kit from UK. TA seems low at 50 ppm. How can TA be low when the pH constantly tends to rise? Is this right?

Presumably we are measuring two different types of alkilinity, doesn't seem to be any other logical explanation?

Anyway, if I now add sodium bicarb in the correct quantity, will it stabilise my pH reading or will I need to do something else too.

It might help to know that I get a lot of limescale deposits, and a tendency to form a slightly slimy scum on the bottom, although the water looks, tastes and feels pretty good. We get a lot of sand blown in from the Sahara, (we are the nearest point to Africa in Europe), but I just vac this out after a bad blow.


chem geek
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Need to understand TA vs pH!

Postby chem geek » Tue 11 Jun, 2013 01:46

Does the pH slow down in its rise when it gets to around 7.7 or 7.8? If so, don't try and lower it below 7.5.

Your limescale deposits getting into the pool will raise the pH and CH as they are calcium carbonate. I would not raise your TA, at least not significantly since that will only make the pH rise worse.

If you have access to boric acid, then you can use 50 ppm borates (as ppm Boron) or a combination of borax and acid. This is an additional pH buffer and while it won't lower the amount of acid you add, it will slow down the rate of pH rise so that you don't need to add acid as frequently. Use The Pool Calculator to calculate dosing.
czechmate
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Need to understand TA vs pH!

Postby czechmate » Wed 12 Jun, 2013 18:01

Boric acid is not a cheap addition to buffer PH fluctuation around 95.00/50 pounds here in Dallas. But the combination of windfall benefits would justify it. At least for someone that maintains his own pool and saves 40 bucks a month on a pool guy.
The fresh gunite, specially plain marcite, will call for acid for at least a year.
I was just gonna mention here, that I finally started using Powdered Calgon to lower my CH and IT WORKS! I have bought several boxes year ago and did not want to waste it on the trial, since I was gonna drain 60% of the volume.
But it was really my borates, that I did not want to lose, so I went 2 years juggling my CSI without draining. This spring I went from CH of 560 to 460 using 3 boxes of Calgon. Even with the CYA at 90, which calls for higher FC, I am managing to be algae free and CSI pretty close to zero, by holding PH around 7.4-7.5.
Culprit is always a correct testing, so I always supplement the different stores tests with my own, than check how much room is there for an error in CYA and CH. (Rising water temperature needs to be also considered).
I also enjoy 2200ppm of salt in my chlorine pool. I think it is good for the water and your skin as well!
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Need to understand TA vs pH!

Postby chem geek » Wed 12 Jun, 2013 20:10

I'm glad the Calgon worked for you to reduce your CH level. Calgon is hexametaphosphate so adds phosphates to the water. At high enough concentrations, phosphates precipitate calcium phosphate. This can be accelerated by using hydrogen peroxide in the water. This is described in this long thread about using hydrogen peroxide for helping to remove metal stains where it was found that it helps in removing calcium scaling and in reducing calcium levels when phosphate levels are high.

As for boric acid pricing, it is $75 for 55 pounds at Duda Diesel , $89.10 for 55 pounds at The Chemistry Store and $60 for 50 pounds at AAA Chemicals . Of course, such prices do not include tax nor shipping.
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Need to understand TA vs pH!

Postby Loongwic » Sun 02 Feb, 2014 07:48

New to the forum have a loooong pool story, trying to be short: Pool built in 2000 initially used our well water for make-up was very hard with both hardness &TA >300 forced to drain pool & acid clean etc! Then made a 6KGal make-up tank & hauled water with our tractor &1500Gal water trailer from the closest municipal drinking water, worked fine until 2010. Since 2010 have a considerable leak have tried/continue to try to reduce/stop the leak(s)! Pool requires make-up water daily in order to operate pool as designed (overflow style). The hauling of water is no longer feasible for many reasons!! Therefore in order to continue using the pool have upgraded our industrial water softener in order to use our well water supply providing water to the pool make-up water tank. Well water initially caused algae problems so then pre-treated the make-up tank water with chlorine & algaecide, solved the algae problem. Having a considerable learning curve to get pool chemistry correct have been using a Taylor Watergram as guidance & Hanna test kits/meters for measurements. Pool pH is constantly increasing to ~8.0 using dry acid to try to both decrease pH & TA. Via the internet have found many articles all say “ideally” need to keep the pH 7.2 - 7.6 with Hardness >150 & TA<120.
In researching this forum with the information specifically provided by “chem geek” recommends targeting a higher pH etc. “If” I am reading the information correctly, as I have a known high TA >300 for supply water can still be able to use while maintaining a higher pH of ~8.0. Have been experimenting with adding dry acid to both pool & make-up water tank to control the pH rising while maintaining desirable TA levels.
Current “pool” chemistry: pH 7.75, hardness 195,TA180 temp 78F.

Please advise best “chemistry” recommended action, given the obvious that need to find & fix the leak(s) ASAP!!
Thank you in advance for your recommendations!!!
chem geek
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Need to understand TA vs pH!

Postby chem geek » Sat 08 Feb, 2014 23:14

Your high TA will tend to make the pH rise though it will slow down in the rise as it gets closer to the equilibrium pH of around 8.7 which is way too high. So you'll need to add acid to lower the TA level. You can either add acid regularly to maintain a lower pH and eventually the TA will drop slowly from the acid addition OR you can accelerate the process through a process of acid addition and aeration of the water all done at a lower pH as described in this post at the top of this forum.

The main risk of higher pH, especially with a high TA or high CH (or both) is calcium carbonate scaling. Fortunately, your CH isn't very high, but you still may see some scaling if your pH gets to around 8.0 or so (which in your case is a Calcite Saturation Index of +0.6). The other issue with high pH is metal staining, but that's not a problem if you don't have metal in your fill water. Well water may have iron, however.

When I talked about targeting a higher pH, that presumed that the TA wasn't very high. If it is, then unless the CH is very low you risk calcium carbonate scaling. So in your situation you really can't just live with a higher pH target (unfortunately).
Loongwic
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Need to understand TA vs pH!

Postby Loongwic » Sun 09 Feb, 2014 21:19

Thank you very much!! I was “hoping” :( the chart provided in this post to lower pH (area in green) indicated a high TA & pH was “somewhat” within desirable limits. Well/fill water tested no iron present & I am seeing slight calcium carbonate buildup on the overflow tiles! As you suggest will continue lower pH &TA by adding dry acid to both pool & make-up water tank to maintain pool chemistry within desirable limits of my watergram which also currently indicated a saturation index of ~+0.6 Thanks again for your response & time!!
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Need to understand TA vs pH!

Postby chem geek » Mon 10 Feb, 2014 00:44

Dry acid increases sulfates. You should consider using Muriatic Acid instead. If you want to avoid fuming, then you can get half-strength acid (15% hydrochloric acid instead of 31.45% hydrochloric acid). Once you get your TA lowered to no higher than 80 ppm (assuming you are using a hypochlorite source of chlorine), you should find your pH not rising so quickly.

As for the chart on carbon dioxide outgassing, the green area is not indicating calcium carbonate scale risk since that also depends on the Calcium Hardness (CH). It is just indicating how over-saturated the water is with respect to carbon dioxide. The green area can still outgas, but less than the yellow or red areas. The actual outgassing rate also depends on aeration so don't take the color coding too literally.
Loongwic
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Need to understand TA vs pH!

Postby Loongwic » Tue 11 Feb, 2014 07:49

Thanks again!! Yes thought maybe my interpretation of the graph was only “wishful” thinking!! :( In any case initially intended to utilize Muriatic acid in lieu of dry acid however expensive & shipment is difficult to our rural address. Now believe I have located a suitable supplier, will give it a try using your guidance. Also “may” have located a contractor that can affect necessary repairs to pool!! If able to reduce/stop the leakage will return to utilizing/hauling the local municipal water as make-up water!! Again appreciate your time & expertise very much!! :)
fred246

Re: Need to understand TA vs pH!

Postby fred246 » Thu 05 Nov, 2015 17:28

so is this boric acid like borax?
how much should I use for 20,000 gallons?

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