Types of Aquarium Heaters

Heaters are essential pieces of equipment for aquariums. Most fish need to be kept in water of a certain temperature range. Tropical pet fish were bred from wild stock that lived in hot jungle areas. Extreme fluctuations in temperature can kill fish, even the hearty goldfish. Four main types of aquarium heaters are available for aquarium hobbyists.

  1. Non-Submersible Heaters

    • Also called hanging heaters, these are the least expensive type of aquarium heater. The temperature control and attachment piece sticks out of the water, while a glass tube containing the heating coils goes underneath the water. The unit has to hang on the top edge of the tank, which can make cutting a hole into a fish tank hood necessary. They are only recommended for freshwater fish, as the sea salt in brackish and marine aquariums can quickly corrode the heater and cause it to electrocute the fish.

    Submersible Heaters

    • Submersible heaters go into the fish tank under the water. They should be turned off when out of the water, such as during water changes, because they may crack or break. Submersible heaters stick to the inside of the wall with suction cups and are often slightly more expensive than non-submersible heaters. They often perform well for tanks of 20 gallons or less. Larger tanks may need more than one submersible heater in order to heat the entire water volume in the tank. They can break without warning, so always keep a spare, according to “The Everything Aquarium Book.”

    Canister Heaters

    • Also called in-filter aquarium heaters, canister heaters are only suitable for freshwater tanks, as the sea salt in other types of aquariums will destroy the heater and possibly kill the fish. Instead of electrocuting the fish as with corroded non-submersible heaters, the corroded metals of a canister heater will leech poisonous chemicals into the aquarium water. Saltwater fish are especially vulnerable to these chemicals. Canister heaters can be equipped with monitors to warn of any problems, but these will cost extra. Canister heaters are often a part of the tank’s entire filtration system, so the water is filtered and heated simultaneously. You cannot buy canister heaters separately from canister filters.

    Substrate Heaters

    • Substrate heaters go underneath the gravel or substrate. They are usually S-shaped cables in order to give heat evenly to the entire tank. A solid bottom of cables would give off too much heat and cook the fish. Aesthetically, these are the most attractive heaters because the gravel hides them completely. They are also good for tanks containing live plants because they can help give all parts of the plant heat. These heaters can be used in freshwater, brackish water or marine aquariums. They are, however, very expensive when compared with non-submersible or submersible heaters.