TA, CO2 gassing off, and pH

[dafletcha]

First off, thanks for this great forum! I'm a new owner of an older pool and am trying to learn all I can. I was especially pleased to find Ben's "secret" for lowering TA.

My TA was at 280, due to frequent topping off with well water (TA=320). (Frequent refills are probably due to a leak, but that's for another post.) I'm in the middle of the low pH+aeration method and the TA has already dropped below 200. I'm confident I can get it down to 100 or so, but I'm thinking about the long term and have some questions:

The well water has a pH of 7.5. If I aerate the water as I add it, will this release any appreciable amount of CO2 in the process--before it gets into the pool?

Also, any thoughts as to how the well water TA could be so high and the pH still be below 8? I've read several posts that say high TA would cause the pH to settle around 8.3. Just curious.

[medvampire]

The well water has a pH of 7.5. If I aerate the water as I add it, will this release any appreciable amount of CO2 in the process--before it gets into the pool?

First off let’s look at the process of dropping ALK by Ben’s method. You use muratic acid to drop the pH witch in turn lowers the ALK then you use aeration to raise the pH back up and the ALK remains at the lower level. Aeration of the incoming water would increase your pH with out benefit of dropping the ALK witch I assume is your goal. I don’t think that aeration of the incoming water will help keep your ALK from rising when adding fill water unless you can acidify it before it is aerated.

Also, any thoughts as to how the well water TA could be so high and the pH still be below 8? I've read several posts that say high TA would cause the pH to settle around 8.3. Just curious.

With out getting a detailed analysis of the well water and even then it may be hard to predict just what the ALK and pH would be. There may be other chemicals in the water that may act as a buffer to hold your pH down. Bicarbonates are just one of the buffering systems in the pool environment but it is the major player.

[dafletcha]

First off let’s look at the process of dropping ALK by Ben’s method. You use muratic acid to drop the pH witch in turn lowers the ALK then you use aeration to raise the pH back up and the ALK remains at the lower level. Aeration of the incoming water would increase your pH with out benefit of dropping the ALK witch I assume is your goal. I don’t think that aeration of the incoming water will help keep your ALK from rising when adding fill water unless you can acidify it before it is aerated.

D'oh! OK, I get it now. Thanks!

[chem geek]

My TA was at 280, due to frequent topping off with well water (TA=320).
...
The well water has a pH of 7.5. If I aerate the water as I add it, will this release any appreciable amount of CO2 in the process--before it gets into the pool?

Also, any thoughts as to how the well water TA could be so high and the pH still be below 8? I've read several posts that say high TA would cause the pH to settle around 8.3. Just curious.

Though medvampire may be correct that other factors may be inhibiting changes in pH in the well water, my guess would be that well water is continually getting saturated with carbonates from the ground that it is in (or flowing through) and that it isn't well exposed or aerated with air which is why it can stay so far out of balance. The 7.5 pH and 320 TA combination gives a relative CO2 outgas rate of about 35 which is quite high. So yes, I would guess that aerating the water as you added it would release some of the CO2 in the process -- but I really can't tell you how much or if it would be worth doing (this is something you could experiment with and let us know your results). You could also add acid to the well water you will be adding to your pool (and then aerate it), but might then need to add back some base before or after this water is put into your pool. I would think it would be whole lot easier to acidify and aerate a small amount of water BEFORE it gets into your pool rather than having to try and lower the TA of the entire pool itself (referring to small refills, of course -- with an initial fill you don't have a choice).

By the way, having the pH rise to just 7.8 reduces the relative outgas rate to about 17 or around half so this is a sensitive process to pH. And this isn't perfect science so keep us posted with your results and good luck!

Richard