I have a 15x48 index pool and been keeping the cover off it lately and letting the water get warmed up by the sun and it usually only gets warm when the days are humid. I'm in nc and the weather temps have been in upper 80s and yesterday it was 100 and the water was warmer. Today it's 80 and water is cool again but not as cold as it has been and not sure when it will be 100 again. Probably July. So I'm wondering if putting the pool cover on will keep the water warmer? It's not a solar cover. Just a black intex cover that came with the pool. Thanks for advice in advance.