What if your pH is low but your TA is high in a saltwater pool?

What are your parameters of "high" and "low"? I will need to know these figures to give an accurate answer. But generally, add small amounts of soda ash frequently, testing between each application and giving each application time to circulate. Thus slowly bringing your pH up. This should not affect the alk. much. Continue until the readings of the pH stabilize at 7.6

Now, taking into account that your alk is high, say above 120 ppm, then you will have to add more acid to adjust the alk to within the proper range. You may have to adjust it to a reading of 70 to 80 ppm. This should have little affect on the pH and they should each adjust with each application of product. You may have to buffer the pH with a little soda ash to keep it from going to lower readings.