I shoot my fountain way up in the air and get the drops to go as far as possible. I have tried day and night, but during the heat of the day, the sun is so hot, that I just do not get much cooling, and I lose a lot of water. I can run 1/2 inch out of the pool with the fountain during one day, and not get any cooling at all. It just slows the rate of heat up under the brutal sun. The night vs day dewpoint is less of an issue in most of Texas (except on the coast). It works better for my area to cool below my desired temp at night, knowing that I am going to gain about 3-5 degrees during the day from just the sun beating down on the pool. So I cool as close to 84 degree F as I can get. The pump stops at 8 am, when the sun hits the pool. From that point, I let the sun heat up the pool, but the top layer insulates the lower levels some. I can get in about noon, and the top layer of water will be around 86 degrees, underneath will be a bit cooler (very refreshing in the heat of the day to feel that cooler water underneath swirling around my legs). We open our big umbrella to shade part of the pool around noon if the wind is not too high. I turn the fountain and pump on about 4:30PM, as that is usually when we get in again, and can stop the temp rise at about 88 degrees for the whole pool (on a good day). We start to get a little shade from the trees at 5:30, and can get a pleasant evening swim at about 88-89 degrees. Leave the fountain and pump running all night, with the solar panels for cooling, and start all over again the next day. The pump runs more than I like, but then, at 105 degrees F, so does my air conditioner in the house.