On a pool forum there is a detailed description of how to lower the alkalinity of water. The key is aeration, bubbling or sort of spraying the pool water to break the surface. The alkalinity will go down but the pH goes up. Add acid to balance it and repeat over days ... in a big pool ...
I have used this procedure on our pool but with our recent addition of a hot tub I have noticed the same cycle of alkalinity going down and pH going up.. Then I realized that maybe I was aerating too much unintentionally. If your air jets are left on when not using the pool it is a wonderful aeration system. So maybe getting the pH in balance and stabile will be easier if we make sure the jets are closed when we leave the tub.