Aquarium Temperature
In our climate, tropical fish tanks need permanent heating under thermostatic control. The thermostat will normally be set at around 25°C (77°F), depending on the type of fish, so in hot weather or in centrally heated homes the heater will not always been operation, having been switched off automatically. The whole system is left on all of the time, and works completely auto-magically. The equipment for controlling the heating of a tropical aquarium is very simple and economical, and extremely reliable.
In its basic form, used for smaller tanks, it consists of a sub-merged unit combining a heater and a thermostat. The heater is large glass test-tube with a sealed rubber stopper, containing heater wire coiled around a ceramic former. A simple mechanical thermostat operates by the bending of a metal strip at various preset temperatures, so that the current is cut in or out, switching the heater coil on or off, and thus the temperature is kept constant to within a couple of degrees. A heat- and waterproof cable runs from the rubber seal out of the tank, and off to the power supply, via a fuse and earth, of course. Both heater and thermostat areaways operated completely submerged; indeed, heaters switched-on out of the water will quickly overheat and may burst.
For larger set-ups separate heater (or heaters) and thermostat is used, with connections made outside the tank via a terminal block, which must be protected from drips. Obviously, the larger the tank, the greater the capacity the heater(s) must have. Usually, for a 901 (20gal) tank, a 100W unit is sufficient; 200W for a 2001(45gal) tank. Specific details are provided by the manufacturers, but remember that, the higher the capacity or wattage of the heater, the greater must be the capacity of the thermostat which controls it.
Some aquarists prefer to use two or more heaters in a large tank. This system provides better heat distribution than a single heater, and also gives a greater degree of ‘fail-safe’ in the unlikely event of heater failure. And some aquarists prefer to use external thermostats glued onto the outside of the glass. These can be simply adjusted to vary the temperature and easily removed for main-tenancy — that is, cleaning the contacts, which ‘become ‘burned after years of use. It is best to replace both heaters and thermostats every few years rather than risk failure and the possibility of the consequent death of your fish.
A thermometer is essential to provide a check on the conditions within your tank. This can be the traditional liquid-filled glass type, attached to the inside of the tank with a plastic sucker, or axial-type stuck on the outside. Most aquarists now prefer a plastic strip containing liquid crystals: this is cheap and unobtrusive. It is stuck on the side of the tank, and indicates temperature by changing colors. Generally, a temperature between 24 and 28°C (75-82°F) suits most tropical fish. At temperatures lower than 20°C (68°F) most fish show signs of discomfort, and chilling may result. This can weaken the fish and make them susceptible to infection. Subtle and sometimes subdued lighting may be necessary to bring out the colours of some fish.