Aquarium Water Heaters
Closely allied to thermostats, as seen from the discussion above, are the heaters. These are essentially small electric coils enclosed in a conduction jacket. This jacket is usually made of Pyrex glass. The Pyrex glass test tubes make the best all around jackets.
It is of the utmost importance that no water be allowed to seep into the heater. If it does, it evaporates when the heater goes on; the water vapor then builds up great pressure in the closed container and is very liable to explode. The pressure is sometimes great enough to blow out the sides of an aquarium.
Of the different kinds of heaters, the submersible type is the most advantageous in principle, although it is most susceptible to explosion. (Should it fail to operate, take it back to the store, as the waterproofing is not guaranteed if the heater has been tampered with.) It heats the water at the bottom of the tank, thus allowing convection currents to heat the tank more evenly than if the surface of the water is heated. Make sure that the heater does not get buried in the sand. Stratification takes place when the top of the water is heated and the bottom is at a much lower temperature. This is a dangerous situation that jeopardizes the health of the fish in the aquarium. Many people advise the use of two heaters, one the regular immersion type, the other the submersible type. This tends to stabilize and equalize the temperature in the tank. Both heaters should operate from the same thermostat.
To calculate the wattage heater necessary for a given tank, allow 5 watts for every gallon of water to be heated. Thus, in a 10-gallon tank a 50-watt heater should be used. Should a lower wattage heater be used, there would be danger that the heater would not give off enough heat to raise the temperature to that required by the thermostat. This would mean that the heater would burn continuously, thus greatly reducing its life span. Using too powerful a heater is just as bad; it will go off and on every few seconds and probably burn out the thermostat.
When hanging an immersion-type, nonsubmersible heater in an aquarium, be sure that the heater is only as far in the water as will safely ensure against the admittance of water into the jacket. On the other hand the danger of having too much of the heater exposed to the air is apparent when you consider the conductivity of water as compared with that of air. Naturally the part
exposed to air will get very hot since air is a very poor conductor of heat and will not cool the glass to any great degree; on the other hand the water will cool off the bottom part of the jacket, thus creating a drastic difference in temperature between the top of the jacket and the bottom. Most glass jackets would crack under the strain. If the heater has a built-in thermostat, the thermostatic unit will probably be located near the top of the heater. Again the consequences are apparent should the heater not be deep enough in the water.
Heaters are measured in watts. The higher the wattage, the more heat it can give off in a given period of time. The wattage you require is determined mathematically, taking into account such things as the lowest temperature in the room in which the aquarium is located, how large the tank is, and how well it is insulated. If the room temperature drops at night, you might consider protecting the sides, bottom, and back with thick styrofoam board. This will keep in the heat.
A 20-gallon aquarium kept at 78° requires a 100 -watt heater if the room temperature doesn't drop below 73° F. If it drops to 68° then the wattage of the heater doubles to 200 watts.
