Actually good to know. I was thinking of making a wireless thermometer that would have several sensors down the length to try and find the thermocline. It probably wouldn’t be terribly cheap, but it would be cool to be able to plot over time.
Redneck Rod poor boy solution - tie ten pool thermometers every X feet on a rope with a weight. Drop it in the pond and go do some chores. Come back later and record the date, time, and the temperature at each depth. I think you would learn the rough movement of your thermocline over the seasons with two years of weekly(?) data.
