Quote Originally Posted by Cords View Post
QUESTION- would the solar cover (somewhat translucent blue bubble wrap) work better if I removed it during the day, and just used it overnight like a blanket? It seems to shade the water and I think the water would warm up better with the sun shining through to the bottom. I think solar cover is a mis-nomer, it is more of an insulated blanket.
Generally taking the cover off during the day and putting it on at night gives you the most heating, but this really depends on the amount of evaporation you get during the day. If your air is very dry or you have a lot of wind (and it's not humid), then your pool may cool off more from evaporation than it would get heated by the sun. As I describe in this thread, around 60% of the energy in sunlight gets absorbed in a typical white plaster pool raising the temperature around 0.7ºF per hour during peak noontime sun if there were no evaporation. However, as I describe in a later post in that thread, 1/4" of evaporation lowers the pool temperature by around 4.9ºF. So which one wins out depends on the evaporation rate. If you are in a humid climate such as Florida, then uncovering the pool during the day is best. If you are in a dry hot climate such as Arizona, then covering the pool would keep it warmer but then again in that desert climate the water is usually too hot and people intentionally keep their pools uncovered to have evaporation help cool them off. If you are in an area with moderate humidity (40-60%) or dry, but you have wind or consistent breezes during the day, then it is probably better to keep the pool covered.

Note that you can get the best of both worlds by using a clear solar cover since that will let at least some of the light into the pool to heat it. The downside is that you will get the associated chlorine loss since such covers usually let UV through as well.