It will soon be time for me to begin opening my pool. Olive in OK where we have hot summers, but over the past two years that I've had it the pool doesn't seem to get warm enough. It gets sun about 70% of the day with one tree sometimes blocking part of it. I don't want to buy a heater, so was looking into adding a solar cover. 1 do they actually work and 2 if they do which one would be recommended? The highest I've ever seen the water get on its own is about 79 degrees. That's fine during the day when it's hot out, but at night no one wants to swim. Thoughts or suggestions? Thanks!