Tropical fish require a normal maintenance temperature between approx. 22-29oC (72-84oF),
with many species being kept at a 'middle value' of 24-25oC (75-77oF). Maintaining a stable
temperature (and more importantly avoiding rapid changes) is vital to avoid stressing fish.
The temperature of a tropical aquarium can be maintained in a number of ways.
Most commonly used nowadays are rod-shaped combined heater-stats, placed inside the tank.
These are available in a number of standard wattages between 25W and 300W. The table below
gives examples of recommended heater wattages for various tank sizes. The modern combined
heater-stats use very reliable thermocouples to maintain a stable temperature.
External thermostats can also be used to control heating elements placed in the tank, and
have the advantage of a less bulky element inside the tank.
Thermofilters are external canister filters which have a heating element built into them.
Many are fitted with a precice temperature controller, which may include a digital readout.
Using a thermofilter avoids having an unsightly heater unit inside the tank.
Heating pads, placed beneath the aquarium, can be used to heat the base of the aquarium.
It is often suggested that heating the substrate is beneficial in planted tanks as it may
promote warm convection currents through the substrate to carry nutrients to plant roots.
Heater cables are often employed for this purpose. These are laid on the base of the tank
and substrate material (often a nutrient-containing type) placed above. Both of these
substrate heating devices are normally used in conjunction with a standard heater.
Recommended Heater Sizes
On larger tanks, it is advisable to use two or more heaters to make up the required wattage -
this not only gives a more even heat distribution, but gives an extra safety margin. If one
heater fails, the other heater will provide some heat and the malfunction should be noticed
before the temperature drops significantly. Also, if one of the smaller heaters should stick
in the 'on' position, it will not raise the tank temperature as rapidly as one larger heater.
The use of a separate thermometer is very important, and it should be checked daily to
verify that the temperature is correct. Although modern heater-stats are very reliable and
can be set to a specific temperature, you will need to verify initially that they are
actually maintaining the correct temperature in the tank, and adjust as necessary. If you
check the temperature every time you feed, you should notice any change in temperature
caused by a failed heater before fish are affected.