So i've been experimenting with how to heat your pool just with the sun. I tried a number of different scenarios and this is the one that worked the best for me.
I go out in the morning around 7am and remove the solar cover. Turn the pump off and let the sun heat it all day. Put the cover back on before bed and turn the pump on and let it filter for 4 or 5 hours.
This increased my temp in my pool ~3 degrees each day i did this. When i left the pump running during the day, i only got about 1 1/2 degree increase. And when i left the cover on, i barely got 1 degree increase.
I have to thermometers in my pool. One is a floater and one sits about 2' down. At night, both read a constant 82 degrees. After the method above, the floater read 94 and the other ready 83. When we went swimming and stirred everything up and got all the hot spots out, both read 85/86ish. The sun heated up the top 6 or 8 " of water rather quickly throughout the day. The next day, i had lost a few degrees overnight. Both read 83. I did the same thing again and after stirring up the pool again, both read 87.
And my tests go along with what most ppl on here say. Cover off during the day, on during the night. I just found it works best when the pump isnt running during the day.
Same tests also showed the best results in my in-laws pool as well.