i was talking recently about this with someone. we have the filter/heater on a timer and set to come on late morning and shut off around 9 pm or so. our property has too many trees so direct sun on the pool is really only from about noon to 5 pm. we use a solar fish, not a cover. the other person was saying that since you would lose more heat overnight , that it would be better to run everything at night and let nature take it's course during the day. we have a 20 x 40 inground pool. does this make sense?