Is stable or warmer/cooler daylight/night temps more efficient?

[shoggoth43]

Is it more energy efficient to maintain a stable temperature throughout a 24 hour period, or is it more efficient to have it a couple of degrees warmer during the day and then cooler at night. I'd like to simulate a warmer sun warmed day temp and slightly cooler temps at night but if it's going to be a more expensive option I'll probably skip it.

 

[EmdeReef]

Temp doesn’t fluctuate too much between the day and night on most reefs so I would try to keep the temp as stable as possible.

 

[shoggoth43]

This will be more of a rivermouth tank so there would be shallow water and day/night temp swings in the wild. I’m just curious from a thermodynamics/energy efficiency standpoint if the temperature swing would cause damage to my wallet compared to where my controller now holds within 1 degree F. I’d probably set it for 5 degrees at most and I’m not even sure if the tank would drop that much overnight where it is now. It’s usually around 78 and the room is no colder than 58 degrees during the winter and it has 500W of heat. Worst case I could probably dig out a Killawatt meter.