We've had the solar cover on for about 4 weeks steady. Ours is cut into five sections to facilitate moving it on and off. During the day I remove one section, exposing 1/5 of the water surface to sun and air.
Water chemistry has held steady during the cover-on phase and chlorine consumption has been as expected. No change in TA. But there has been a slow downward drift in pH. The pH has been at 7.5 for the entire season, rock steady, but has been slowly moving downward over the past 4 weeks and measured 7.2 this morning.
Why does the use of the solar cover seem to result in a pH drop?