TA - Total Alkalinity
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.
You can raise TA with baking soda. It is often best to make large TA adjustments in a couple of steps, testing the water after each one, as adding large quantities of baking soda can raise the PH a little and you don't want the PH going out of range.
21,000 gallon inground
Haywood Sand Filter
Have a look at this for an intro to pool water chemistry, Pool School - ABCs of Pool Water Chemistry
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