Eric,

Though you have reduced the measured Total Alkalinity by adding acid, you actually haven't removed hardly any of the carbonate from your pool. My calculations show that simply adding acid to lower the pH from 8.2 to 7.2 will lower the TA from 180 to 157 just by changing the proportion of different chemical species in the water (you shifted to having more carbonic acid, H2CO3, in the water and that species does not count towards TA). If you were to raise the pH even by adding caustic soda / lye (which does not have carbonate), you would raise the TA back up again. pH and TA move up and down together.

This is why adding acid alone does not really lower the TA in an absolute sense. Only the aeration will do that and aerating while at a lower pH gets rid of the carbonate in the water faster. So when you get your waterfall fixed, start aerating while keeping the pH low and that will truly lower the amount of carbonate in your pool.

Richard