Surface temp was - 80*, bottom temp was - 78-79*, this was at the time when Diffusers were in the deepest holes and outdoor temps in the 90s.
About this time a couple years ago, Bob wrote an article where he talked about Aeration and Thermocline temp. The take-away I got from it was, a Thermocline temperature refuge is just as important as Aeration, possibly more so, for fish health.
Makes sense to me, if they have no escape from 80* waters, they'll suffer. Since then, my diffusers are a few feet above the deepest holes, and a timer is enabled when outdoor temps get near 90* for more than a day. In my area, we might get a few weeks a year above 90*. Meaning about 50 weeks a year, it runs 24-7. Only the deepest diffuser is turned off in winter.
