The easiest and cheapest way to cool your pool is to put a fountain in it. There are many types available which can connect to your pool's return line. By spraying the water into the air some of it will evaporate, drawing heat out of the rest of the water and thereby cooling it down. This is the same method employed by the old water cooling towers you used to see on top of buildings.
You will get the best effect if you run the fountain at night, taking advantage of the cooler temperatures that will also help cool the water. Yes, you will lose more water to evaporation than normal, but this will be a small price to pay to increase the enjoyment of your pool. The increased use of the pool can save on water by reducing the number of showers taken by the family with a net result of saving on water.
