Lowering the pH by adding acid to the fill water AND aerating will lower the TA and that is easier to do with the fill water before it gets into the pool than trying to do this after the pool is filled. But that's for lowering TA, not CH. I don't see how adding acid will have any affect on the Calcium Hardness (CH) of fill water. Nevertheless, if you have high CH in fill water, you can compensate for that by having lower TA. You don't need much TA (as low as 50, depending on CH level) if you are using bleach or chlorinating liquid as your source of chlorine.
Richard
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