Ph v ta

[chem geek]

I don't think I can take credit for that explanation since I believe waterbear (Evan) was the first to explain it that way though it's been so long that I don't remember exactly who said what first -- not that it matters.

[Watermom]

Where is Evan, by the way? I was thinking about him the other day and wondering where he's been.

[chem geek]

It is not high TA by itself, but a combination of high pH, Total Alkalinity (TA) and/or Calcium Hardness (CH) that can produce scaling. It is the opposite of having these parameters be too low where plaster can dissolve. One can use The Pool Calculator:

http://www.thepoolcalculator.com/

to enter one's pool water parameters and calculate the saturation index. If this index is very negative than the calcium carbonate in pool plaster can dissolve into the water while if the index is very positive, then the calcium carbonate in the water can cause scale onto the pool plaster or can cause cloudy water.

The ideal is to saturate the water with calcium carbonate so that it neither dissolves plaster nor creates scale. Though a saturation index of zero is technically ideal, anything in the -0.3 to +0.3 range is usually fine and in practice one doesn't see scaling until one gets up above around +0.7 (though in spas one can sometimes see this above +0.3).

The main problem with a high TA by itself is that it tends to cause the pH to rise over time due to carbon dioxide outgassing from the pool. Pools are intentionally over-carbonated and TA is a measure of that carbonation. There is more carbon dioxide in the pool water than the equilibrium amount there would be from being exposed to air so carbon dioxide regularly leaves the pool and this causes the pH to rise. When the TA is higher, this occurs more quickly. It also happens faster when the pH is lower and when there is more aeration of the water (waterfalls, spillovers, fountains, heavy rain, lots of splashing, returns turned upward, etc.).

What you wrote in your post was perfect. You are managing your CSI to not get too high and therefore the only effect of the higher TA is to have the pH rise over time. You are adding acid to keep the pH down and over time the TA should be dropping. As this occurs, you are adjusting your CH to compensate and keep the CSI near zero. This is exactly what you should be doing. Another alternative would be to do the lowering TA procedure to speed up the process by lowering the pH and aerating in addition to adding acid, but you'll end up using the same total amount of acid -- it just accelerates the process so that when you are done the pH is more stable. It's a personal choice which way to go.

[waterbear]

I don't think I can take credit for that explanation since I believe waterbear (Evan) was the first to explain it that way though it's been so long that I don't remember exactly who said what first -- not that it matters.

http://www.poolforum.com/pf2/showthr...9434#post49434
My first post in the thread about halfway down in bold.

[CarlD]

Who remembers???

"Old Timer's Disease" is catching up with me.

[waterbear]

Who remembers???

"Old Timer's Disease" is catching up with me.

'Sokay. I have CRS disease (Can't Remember Sheets)
There ARE ways around the dirty word filter!

[CarlD]

'Sokay. I have CRS disease (Can't Remember Sheets)
There ARE ways around the dirty word filter!

Ben calls it BS--Barnyard Slush!