Solar cover on or off during day to gain heat?

[gonzapa]

I basically have the same question as I want the temperature as high as possible and no one uses the pool till 5 pm in the afternon

[CarlD]

I believe that convection and evaporation will cost you more heat during the day than you gain by reducing exposure to sunlight. I see my clear cover as a greenhouse--the cover prevents convection heat leaving and reduces evaporation.