Not enough circulation - water not at uniform temp

[TheBigBlueFrog]

Our pump thermometer and our heater thermostat are both reading near 80°F, but our floating thermometer is reading a full 10° lower. My son went swimming yesterday, and he said the water at the bottom is definitely warmer. Is it normal for the cooler water to be at the top? This seems to go against everything I've ever learned about thermodynamics. I thought cold water was supposed to sink, and warm water was suppose to rise. I plan on running the heater to raise the temperature of the water, but do I also need to redirect the jets to increase surface circulation, or is this just overnight cooling affecting the surface water? Our highs right now are in the low 80's, and lows in the mid-60s.

 

[mknauss]

I assume you do not cover the pool with a solar cover or other. Evaporative cooling at night when water is much warmer than the air temperature does lower the water temperature pretty dramatically. But as you said, it should flip around if the colder water is on top of the warmer water.
Do you not run the Polaris cleaner?

 

[TheBigBlueFrog]

I run the Polaris a few hours in the morning, and a few hours in the afternoon. We have a cover, but we haven't been using it since the temps got above 60° at night. Might have to rethink that.