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Tropical fish usually require water to be about 78 degrees Fahrenheit. There are species of fish, however, that require 74 - 84 degrees Fahrenheit. A heater that is thermostatically controlled and the correct wattage is a must for your fish.

Basic Heaters

The most basic heater will have an electric element inside of a water-tight glass tube. When the water temperature drops, the heating coil will automatically be turned on by the thermostat. There are two types of thermostats, an internal thermostat is within the glass tube; an external thermostat will be attached to the outside of the aquarium. Units that are combined are easier to connect. The type you select is a matter of preference, but any unit needs to be submerged at all times and clear of gravel allowing the water to circulate completely.

Heater Size

The correct size is very important; a small heater will run constantly and soon wear out, requiring replacement. A good rule of thumb is that each gallon of water should have 5 watts of power. If you have any questions concerning the wattage you need, inquire where you are purchasing your heater. Aquariums over 3 feet long are best heated with 2 units to ensure evenly heated water.


Since water temperature needs to be constant, an aquarium thermometer is necessary. Attach a floating thermometer to the inside of the tank with suction pads. There are also thermometers that fasten to the outside of the tank. If you purchase the liquid crystal type do not put it in direct sunlight, it will affect the reading. A darker or shaded area of the tank is best.

Setting Temperature

After you have placed the heater in your tank, start it at a low temperature reading and slowly advance to the desired temperature, using your thermometer as you go. When you reach your desired temperature it is vital to keep it there - quick changes in temperature can not only cause stress, but can also cause disease or even death.

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