Acid and Alkalinity up Loop

I have a salt 10K gallon pool in south Florida and having a hard time keeping my pH and alkalinity in range. I have great luck just keeping the pH at 7.5 by adding 2 cups of acid a week. When I tested the alkalinity, it was reading around 30 so I added baking soda and brought it up to 80. But now I have to add more acid to keep the pH in line. Doing that makes alkalinity go down.

Sounds like basic chemistry to me.
Now I’m caught in an endless loop.

How do I keep the alkalinity and pH in range at the same time?