I set the heaters in my tanks to 75°F.
In the summertime I would turn the heaters off completely and just let the tanks ebb and flow with the air temps ( no AC ). Tanks would fluctuate from 77° at night to 88° (on the hottest days).
Winter I plugged heaters back in and set to 75°. Low enough to slow metabolism a bit, but not so low to make them lethargic.
Here is my Amphilophus Saggitae in 75°F on February 25 2021