What temp?

[LizStreithorst]

At what temp should I keep the temp of my fish room to keep the water in the tanks at 83?  I suppose it takes a higher ambient temperature on a 120 than on a 20, right.  What I think I really need are temperature controllers.  Rick posted about making a home made one on Simply.  It involved soldering and wires and it was over my head

[BillT]

The temperature in a body of water in an atmosphere of a given temperature will depend several factors.

If the water is just sitting there doing nothing, it will equilibrate to the same temperature in some period of time (longer (like days) for a large tank).

If evaporation is occurring, the water temperature will be less since heat is removed from the water by evaporation.

I have tested covered beakers (glass wall) holding 100 mls of water. They were about 2 degrees below ambient temperature. Because they were covered evaporation was reduced because the atmosphere under the cover had a higher humidity for the evaporation to work against. Uncovered in a lower humidity room would reduce the temperature more.

If water of a lower temperature is added, there will be a race between adding cooler water and heating from the ambient air temp.

Insulation on the tank, aeration, humidity and water motion are additional factors.

This would not be easy to calculate.

I suppose it takes a higher ambient temperature on a 120 than on a 20, right.

Depends: The 20 has more surface area for temperature exchange to its volume (amount to be changed) so it should change faster. However, it may also evaporate more and lose heat faster (more (evoparative) surface area to volume also works here).


Instead I would set-up an unheated tank of your average size (or perhaps several sizes) as you would your other tanks.
Put in a thermometer and see what happens.
The offset from the room temp will probably be a decent predictor for the other tanks.