pH TA relation question

[AV8TOR]

My tap water is pH 7.2 and when we bought the house the TA was 110. I have brought the TA down to 90. My question is does a higher TA raise the pH more than a lower pH? Seems like I adjust the pH to 7.5 but in 3-5 days it starts to rise again. I lower never let it go above 7.8. What is raising the pH?

CA is 280
CYA 50

 

[JasonLion]

Dissolved CO2 is outgassing to the atmosphere, which raises the PH. The higher the TA level and the more aeration you have, the more quickly this happens.

Pool water is maintained out of balance, with excess dissolved CO2 (like carbonated soda), to get the TA and PH where we want them to be for swimming. The reactions that put the water back into balance, CO2 outgassing, are slow. As the CO2 outgases, the PH goes up. The higher your TA level, the more out of balance the water is, so the more quickly CO2 outgases.

There are actually a couple of other reactions that can take place which can move the PH around. But CO2 outgassing is usually the dominant effect.

 

[AV8TOR]

So in a nut shell then if I lower the TA even further, say to 70 the pH will rise less or is the effect of outgassing the same and will still raise the pH as it did?

 

[Guest]

Lower TA means less outgassing
ta-what-is-it-really-t4979.html

 

[chem geek]

This table shows how lower TA and/or higher pH have a pool be closer to equilibrium with the air in terms of carbon dioxide, so less outgassing. The rate of outgassing is apparently more related to the square of the TA whereas the table is just showing the linear concentration ratio. So the effect of lowering the TA to reduce the rate of pH rise can be quite dramatic. The color coding in the table is very rough where a pool's specific situation, in terms of rate of pH rise, will depend a lot on the amount of aeration. A pool cover helps a lot at making the pH more stable even when the TA is high; a waterfall/spillover makes the pH tend to rise faster.

Richard

 

[AV8TOR]

Thanks guys just what I was looking for