If the pH in a spa tends to rise, then keep the TA lower and target a somewhat higher pH (say, 7.7). If you are using Dichlor, then that is net acidic when accounting for chlorine usage/consumption. You can minimize the pH rise not only by keeping the TA lower and target pH higher, but also minimizing the amount of aeration in the spa (i.e. spa jets). If you want additional pH stability, consider adding 50 ppm Borates to the spa using boric acid (as in products such as Proteam Gentle Spa).