how much does your tank temperature fluctuate

Just wondering how much people tank temp fluctuates ? Do you have to change the temp on the heater coming in to summer/winter ? How much does the temp change throughout the day ?
The reason I ask is because my tank seems to vary by 1oC over 24 hours. goes between 29.5 and 30.5

wat fish are you keeping?

What have you got the heater set to? If it is going below that then hte heater will stay on until it reaches the determined temprature.

What size is the tank and how many watts is your heater?

Mark

When I had my 400ltr freshwater setup I hardly noticed any change during the day or night. Its now a salty setup and things are different. The temp seems to go up by about 1.5 degrees in the afternoon then it seems to drop below the set temp by about half a degree. My heater seems to be on a lot then to get it back up to the desired temp. This happens daily and Im yet to go through a winter with this salty setup so to be honest Im a little concerned. My living room does get warm during the day so I guess that would explain the rise but it never happened to this degree with the freshwater setup. It probably has something to do with the different chemistry of the water but what do I know. I had been meaning to post up a thread on this issue myself so if any of the scientists here have any ideas...(in laymans please) .

Jay

1- For the same volume of water, one fresh, one salted, which one holds
more heat? The answer is fresh water.
Pure water has the highest specific heat (the amount of heat needed to
raise the temperature of 1 kg of a substance by 1 degree C). Addition of
salt reduces this heat storing capacity.

2- For the same volume of water, one fresh, one salted, which one boils
later (i.e., at a higher temperature), and thus can hold more heat prior
to boiling and evaporation? The answer is salt water. Adding salt to
water raises its "boiling point", which is the temperature at which it
boils. The reason for that is that salt molecules, acting like tiny
magnets, tend to hold the water molecules down. Water molecules then need
more energy (thus higher water temperature) to be able to escape (evaporate).

There seems to be a myth (I think!) that salt water "holds" heat (whatever
that means.) better than fresh water. On either a mass or molar basis the
heat capacity of the two are quite similar as is their thermal conductivity.
So I ask, "Show me the data that indicates that the two have very different
thermal properties."

Hopefully you can glean something from this Jay.

Kev.

Thanks for that Kev, very informative. Im wondering if I mabey insulate the tank a bit would it help to regulate the temperature more efficiently. Anyhow, thats a load off my mind so thanks again .

Jay

I thought it interesting too, I'd definitely try insulating, it doesn't need to be thick, 3/4 inch poly will be enough.

Kev.

Sweet, have some in the shed. Cheers bro.

Jay

@Kev...Good stuff there....and I did some calculations whilst eating my tea.

The thermal properties (at the temperatures we keep fish at) tend to be much of muchness for seawater and pure water; if we convert volumes to mass (as it should be) then the differences do tend to get closer. Specific heat capacity should be 'per kilogram' (so volume per volume, seawater has a greater mass hence a given volume has a higher mass to 'hold' energy).

Kev, now stop tempting me to be nerdy.

Where we may see some bigger divergences would be at the relevant freezing points....but I'm not going there.

So, Kev has explained the water differences, and added to that would be other items:

the natural 'hysteresis' of the thermostat. In simple terms, this is the lag between a thermostat switching ON and OFF (ie what temp does the thermostat allow a drop before switching back on, and at which temp above the set temp does it switch the heater off).
Different heater designs have different hysteresis'....electronic or bi-metal strip.

If, for some reason, there is a proportional (either pulse or dimmer) then they work on a different principle.

Other items that come into play are heat loss or temperature gradients (covered in an above thread in insulation), water circulation, and decor and glass (eg rocks not only have a different specific heat capacity to water, they also reduce the mass of the water), the degree of evaporation and degree of condensation (but they are probably not going to affect the temp drops too much on a bulk scale). Lighting will also affect temp (of course)....but I won't go into the energetics of biological processes because that would be getting too silly.
And heater wattage and tank volume have already been covered in posts above.

For riverine fish and small lake dwelling fish, I'm happy with large diurnal temp changes. But would be concerned about marine temp changes of any note.

(back to my calculator....not)

ian