Aquarium Heaters are required when keeping tropical fish. Room temperature water is not even close to that of their original habitat. Tropical freshwater usually stays above 70°F.
That is because you are dry and warm-blooded. Your little friends are wet and cold-blooded. This means they don't produce their own body heat and what heat they have comes from, and leaves to, the water around them.
You know you need an aquarium heater when the room temperature stays below 80° or or changes more than 2° between night and day. As a general rule, you will need a heater.
When buying a heater, always check the labeling. Good heaters will have a label that tells you what size tank the heater works in. That doesn't mean you only need one.
In tanks that have a reasonably large water surface, two heaters may be needed if you like to keep your house cool or it is wintertime. A fish tank larger than 40 gallons probably needs two heaters, even if the labeling says the aquarium heater is rated for your tank.
It is not a requirement, but you should get a thermometer for your aquarium. I like to use one that is actually in the water because the type that stick to the outside of the tank are not as accurate.
Why would I need two heaters?
Fish tanks with a large water surface bleed heat at a fairly quick rate. A single heater, even if rated for your tank size, may not be able to keep up with this. Placing a heater on opposite ends of the tank will solve this problem in most cases.
Another way to ease your little buddies' suffering is to place your heater in the path of your aquarium filter's outflow. By running water close by your heater, you move heated water around the aquarium instead of having it radiate from one spot.
We all remember the horror stories when we were young about dropping radios and hairdryers in a bathtub. Our Home Economics teachers would say it every year, like any of us would really do something so ridiculous. So it seems to reason that we shouldn't be putting an electrical appliance with a heating element underwater.
Most, not all, heaters are fully submersible. Again, check the labeling. Make sure that you are not buying a heater that you cannot put underwater. Most heaters have a thermostat knob on them. You want one that is sealed up so that the entire heater, body and thermostat knob, can be underwater. If it does not say the word "submersible" someplace on the label, you and your little wet friends might ride the lightning.
This can be lethal.
You may be tempted to buy a cheap heater because a good one will cost a little more. Don't do it. Cheap heaters have cheap thermostats and thin glass. You run the risk of the heater being stuck in the on position and cooking your fish. There is also a remote chance that a fish could dislodge it and break the glass. Especially if you have a large cichlid. Those guys like to rearrange the aquarium for you. A little fish fung shui.
Another reason not to buy a cheap heater is that you will have to replace it in about a year. Cheap heaters tend to just stop working after that long. A good heater will save you money over time.Look our affiliate partner's website to find the right aquarium heater for the health and safety of your little friends.
For details about how an aquarium heater works, check out Wikipedia's Aquarium Heaters page.