I hear most people need to constantly add acid to their pools as the pH rises. The pH of my pool always goes down. I have never added acid and am constantly adding washing soda. Typical test results:
FC: 3 to 6 ppm depending on the time of day
CC: 0 ppm
TA: 80 ppm
CYA: 40 ppm
I'll bring the pH up to 7.6 with washing soda and over about 10 days it drops again to 7.2. Repeat every 10 days. Pool is kept covered when it's cool out and uncovered when it's warm. I notice no difference in the rate of pH change with the cover on or off.