When the pH is very low and the TA is essentially exhausted, then baking soda will raise both the pH and the TA. However, one must be careful not to overshoot the TA level. With pH Up (soda ash; washing soda) one can raise the pH faster with less likelihood of overshooting the TA. If I start with a pH of 7.5, TA of 100, CYA of 30 and add 8 gallons of acid to 30,000 gallons, then I end up with a pH of 3.2 (and TA of -30; carbonate alkalinity near zero), then adding 80 cups (50 pounds) of baking soda raises the pH to 6.4 with the TA at 86 ppm. In reality, less would need to be added since some of the acid would dissolve scale, but the point is that if one continued to add baking soda one could overshoot the TA. Of course, one could aerate to raise the pH but that can take a while. If instead one added 56 cups (32 pounds) of pH Up, the pH would rise to 7.5 with the TA at 88 ppm.