confusion about TA..

[link147]

Hi everybody!! (Hi doctor Nick!)
Couldn't resist.

Anyway, I have a question about TA and it's purpose. So, I am catching up on all the post that I missed while I slept (am I the only one that sleeps on this website?), and I saw a post by chem geek:

Total Alkalinity (TA) Myths
Myth: Increasing TA lowers rate of pH rise
from this post: http://www.troublefreepools.com/viewtop ... highlight=

I thought that TA slowed pH rise by acting as a buffer. I did some looking and saw this by Jasonlion (thanks for poolcalc):

Total alkalinity indicates the water's ability to buffer PH changes. Buffering means you need to use a larger quantity of a chemical to change the PH. At low TA levels the PH tends to swing around wildly. At high TA levels the PH tends to drift up slowly, or even quickly in extreme cases.
from this sticky: http://www.troublefreepools.com/about2375.html

I know both people are very knowledgeable, and I don't doubt either (they are both WAY smarter that I), but I am confused now.
I guess my question is what does TA do?
Thanks,
Link

 

[JasonLion]

There are really two different effects. TA buffers PH changes from external sources, so it takes more acid or base the change the PH by a given amount. TA also has a "natural" PH of around 8.4, so the higher the TA the more pressure there will be from the TA it's self to push the PH towards 8.4. How much the PH actually moves depends on the amount of aeration. Low aeration will mean very little PH movement from TA, high aeration and high TA means lots of PH rise.

When you are using trichlor for chlorine, the trichlor is acidic and high TA levels work very well to control the PH change. Not only does the TA slow the PH decrease from the acidic trichlor it also provides some of it's own upward pressure on TA to balance the downward pressure of the trichlor. When you are using bleach there is no long term pressure on PH from the bleach so the TA level can be lower. When using a SWG, the SWG provides aeration and doesn't push PH around so it becomes important to keep the TA level fairly low.

 

[Guest]

This sticky and this thread might be helpful in explaining things.