Heating aquariums - thermostat settings and temperature

tanker

I've ended up with three small (20L) betta tanks added to my fish menagerie. It's autumn and starting to get cool at night so I've been studying the temperature settings to ensure that everybody's warm enough. I have 25W Aqua One heaters in the tanks. The box said that that size was suitable for up to 25 litres.

The actual temperature in the tanks seems to be significantly lower than the thermostat setting on the heaters. For example, the temperature was showing as around 23 degrees, so I turned up the heater to read 28. At a setting of 28, the real temperature is around 25 degrees. (I'm pretty sure the measured temperature is accurate. I've glass thermometers in the tanks, but I bought a digital thermometer that goes in the tank, and I've measured them with that as well and get an equivalent reading to the glass thermometers' readings.)

Is this to be expected? Does it mean the heaters are calibrated incorrectly, or (too?) small for the tanks? Is there any problem trusting the thermometers and having the setting on the heaters set higher? Also, do you have to fiddle with the heaters at the change of seasons or will they be stable once you find the right thermostat setting regardless of the external temperatures?

Thanks for any help.

iamntbatman

That's not really uncommon. In a few of my tanks I have to set the heater either higher or lower than the thermometer reading. I think calibration issues are usually to blame.

rsn48

Ignore the displayed settings on the heaters and instead - ssssllllllooooowwwllllyyyyy - turn it up to get your desired temp. I've just been through a bit of a problem which was resolved when I moved the heater away from the vertical position, to an angled position. The heat will rise up the sides of the heater and the internal thermometer reads that water, not your aquarium water in general.

tanker

Thanks. I'll go by what the thermometer says. It just threw me because of the size of the difference in tank temperature from the set temperature and also that it was doing it in 2 tanks (the third seems more in line with the set temperature).

Byron

I agrtee with both iamntbatman and rsn48. I have same issue, but with mine the heater setting has to be lower than the temp it creates; I worry that the heater is even OK when I see this, but keep an eye on it. And glass thermometers floating are more accurate than stick-on. I like two thermomenters in my large tanks just for security on accuracy.

tanker

Thanks. I re-read the instructions and I also had the bottom suction cap too low on the heater, so that might have been contributing to it.