Originally Posted by Wendyjo
Not sure I agree with this. In my experience larger volumes of water will keep a steady temp better than smaller ones. For example. when I lost power during the recent hurricane my small tanks (2.5 and 5 gallons) dropped 5 or more degrees in about 6 hours. My 40g dropped about 2 degrees in 12 hours. Same deal when I lost power in the summer - my small tanks got hot pretty fast where as the large tank kept it's original temp of around 78 degrees thought out the power outage. All tanks have lids and are in the same general area of the house. Small volumes of water are not as stable as larger volumes of water.
Fill up 1 gallon bucket and a 5 gallon bucket with the same temp water, and treat them the same (i.e. expose them to the same external temps and either cover both or leave both uncovered) and the 1 gallon will experience a more drastic temp change.
All my 5g hold a steadier temperature compared to my 40g. Part of the reason is equipment used. I know some small tanks come with florescent lights which I am sure would cause the same issue as they do in larger tanks, but smaller tanks more often are sold with cooler burning LEDs.
Smaller tanks tend to be acrylic now as oppose to big tanks. My 5gs are acrylic and my 40g is glass as well as my retired 20g(was in the same room as my 5gs) which also had stronger temp fluxes then my 5s.
I know that evaporation factor plays a strong part here near LA. My 40g can flux as much as 5 degree swings in less then an hour without my heater or chiller. My 20T only had a 3 degree drop but I use LEDs with it. My 5gs only drops by 2 degrees when it gets cooler outside. Only a room apart but both rooms have a similar lay out as to windows and doors into the room.
Again I will state I do not know the full story on the tanks that were used. There are a lot of factors that can play into these questions asked. I am just basing my guess off the most likely scenario given the ease of getting glass/florescent vs. acrylic/LED tank types.