I know this has been stated alot already but I feel I need to say it again. in the natural enviroment the temp swing is gradual and over time and as you said the water is a few meters deep in a tank most if not all the side are exposed to the air not to mention most tanks are on stands this means that the tank will cool much faster even with a gradual air temp change, basic hydrothermal processes.
also I see you live in TX, kinda warm there isn't it? we all don't live where it's very warm, I live in VT (yes thats a state not a city) where at this time of year it's still in the 60's and 70's during the day but is dropping to the 40's and even the high 30's at night, now this doesn't really affect us humans we put on a sweater throw an extra blanket on the bed as we are not millionairs who can just crank up the heat when ever so a small heater that uses next to no energy is worth the health of our fish, also just cause a fish can live at say 65f it might not spawn till 80f so a happy inbetween is often desirable
also I see you live in TX, kinda warm there isn't it? we all don't live where it's very warm, I live in VT (yes thats a state not a city) where at this time of year it's still in the 60's and 70's during the day but is dropping to the 40's and even the high 30's at night, now this doesn't really affect us humans we put on a sweater throw an extra blanket on the bed as we are not millionairs who can just crank up the heat when ever so a small heater that uses next to no energy is worth the health of our fish, also just cause a fish can live at say 65f it might not spawn till 80f so a happy inbetween is often desirable
