I have gotten mixed answers on this question so i would like more feedback. We are in Indianapolis. Right now highs are in mid 70s lows in mid-hi 50s. Upon pool opening water temp is 63 degrees. We have a heat pump which is more efficient as ambient air is at 60 degrees or higher. Therefore we are running the heat pump in daytime hours only. My question: On a sunny day with temps between 70-80 degrees, heat pump running, should the auto cover remain closed or open? I can see the logic in both but wanted to know if there are facts to support which is more effective in raising water temp faster. (We obviously keep cover closed at night)