Anecdotal information follows:
.35 acre pond. Not a typical bowl-shaped basin. Gently sloped down to ~6' then sheer drop into 12' on the south and 16' on the north.
During the warm season I run air from midnight to 7:00am.
Single diffuser set 4' off the bottom in ~16' (full pool) of water.
I typically see ~7°-10° delta between surface temps and 10' deep temps.
In June I was seeing 80° surface temps with 69° at 10'. The weather at that time was generally wet and cool.
Last month when it was close to 100° for days on end the highest surface temp I saw was 88°.
10' deep temp was 84°.
Three weeks later the weather has moderated, we've gotten some rain, and my surface temp has dropped to 77°.
10' deep temp it's 71°.
