This will increase water loss by evaporation however + will require at least part of the water to remain uncovered, also leading to water loss. Ive heard of some people in hot places losing up to an inch of water in a week without a tight fitting hood. Just my 2 penneths worthsome people think that you should always drop temp slowly. Turn your heater down about 1 click a day until it reaches the temp you want. If you live in a really hot climate and have trouble keeping the temp down then you can use a small fan directed across the surface of the water. This tends to cool the water pretty effectivly IME. It's a bit tricky to keep the temp stable with this method but it's certainly cheaper than the SW chillers you can buy.