David, Acids will become bound to sugars during the pasteurization process. For this reason testing the acidity or pH of a kit wine will not give accurate results.
I would suggest testing and adjusting the acidity of a scratch wine at the time the must is prepared. Also, the wine should be tested during bulk aging and adjusted when racking. During fermentation, the acidity may decrease by 0.05% to 0.10%. If the wine goes through a malolactic fermentation, there may be another 0.05% to 0.20% reduction in acidity.
Until you develop the expertise to determine acidity by taste, I would suggest using the acid test kit. The sugar present during the preparation of the must can be confusing to the taste buds.