Ph and TA relationship


LifeTime Supporter
Apr 5, 2007
Joliet, Il.
Hi all,

I thought I'd move my questions into its own post instead of continuing in the other thread.

Rangeball said:
I would add "unless your elevated TA causes PH increases as chlorine is less effective at higher PH levels as well as potential water clarity issues from higher PH."

Rangeball said:
Chemgeek has a chart here somewhere that shows the outgassing and PH increase at different TA levels. Generally, the higher the TA, the quicker the PH rise.

This is also how it works in my vinyl IG pool. If TA get's much above 150, PH creeps up on an almost daily basis, daily if TA is 200+.

I have it at 120 now, and it is holding fairly steady, creeps up every 2-3 weeks or so.

chem geek said:
Since you are not using an acidic source of chlorine (i.e. you are on BBB), you can lower your TA level more. With your lower CYA, you can lower your TA down even to 60, though try out 80 or 70 first to see if it makes a difference. It will likely reduce the amount of acid you need to add but may only have a small effect on the rate of pH rise.

Every place I've read talks about the Ph bounce associated with low TA and high TA causing resistant changes.

gonefishin said:
I'd agree that chlorine is less effective as the Ph rises. But isn't the Ph bounce caused from low TA readings and not high readings. From my understanding high TA levels make the Ph more resistant (and sometime stubborn) to change the Ph level. High TA readings would be over 200. With a reading of 170 in a vinyl pool, I don't see any reason to make a TA change unless he's having a difficult time making a necassary change to his Ph.


Below is a quote out of the CPO instructor manual. I've put in bold a couple of points that I have questions about.

[size=4]Certified Pool-Spa Operator® Instructor Manual © National Swimming Pool Foundation® 2007[/size] said:
Key Points: Discuss the various aspects of total alkalinity. These include:
Total alkalinity is the measure of the ability of water to resist changes in pH.
The acceptable operating range for total alkalinity is 60-180 ppm.
The ideal operating range for total alkalinity is 80-120 ppm.
The measure of total alkalinity (TA) may need adjustment if products with cyanuric acid (CYA) are used. To adjust alkalinity, use the following formula:
Adjusted TA = TA - (CYA ÷ 3)
At low total alkalinity level, there may be little or no buffering of water, allowing the pH levels to fluctuate drastically.
At high total alkalinity levels, there may be an over-buffering of the water, making it very difficult to make chemical changes in the water.
I'm trying to get a better understanding between Ph and TA in the context above. I've read many times here and at poolsolutions that the higher TA will cause Ph to rise, yet everywhere else talks about low TA being associated with Ph bounce and high TA being associated with difficult to move levels (instead of quickly rising levels). I've seen a couple times where numbers as low as 60 or 70 are recommended, that's awful low isn't it?


The buffering ability of bicarbonates works better at preventing pH drop than pH rise, thus a higher TA is effective at preventing pH bounce with acidic chlorine sources but less so with alkaline chlorine sources. This is the reason that a lower TA is recommened for unstablized chlorine, usually 80-100 ppm and that is what is in the CPO study manual that I have. There are several providers that do the CPO exam and there is slightly different information in the various books that I have seen. The info from the one you have is very oversimplified and that can be seen in their formula for stabilizer corrections. Subtracting 1/3 the cya reading only holds true for pH beween 7.4 and 8.0 and is still an approximation. For pH from 7.0 to 7.2 1/4 the cya reading is closer to the actual value.

IF the TA is too low then there is not enough buffering effect and pH can become unstable but the general tendency of a high TA will be for the pH to move toward about 8.2 if no other chemicals are added to the water. If you are adding an acidic chlorine source this is adventageous but if you are using an alkaline chlorine source you want to slow this pH rise down and by having a lower TA that will occur.

This thread at poolforum might explain a bit more!