Functionally, "total alkalinity" or TA is the resistance to change in pH possessed by a particular sample of water.
Lowering carbonate alkalinity (the portion of TA caused by dissolved carbonates and bicarbonates) is covered here: http://pool9.net/alk-step
Generally speaking, you can't lower TA in a covered pool, unless you have a mass aerator in action, such as an ozone venturi or a spa jet in the steps.
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