A heater is an essential piece of equipment for a tropical marine aquarium. Here is what you need to know to pick a good one for your system.
Aquarium heaters are essential equipment in the tropical marine aquarium hobby. Remember that tropical marine fish generally inhabit oceans with temperatures greater than 20°C. This is because, as was explained in this article, reef-building stony corals are confined to living between the 20°C isotherms. Most of these corals thrive when water temperatures are between 23- and 29°C, and most marine aquarium hobbyists keep their tropical marine tanks between 25- and 27-°C.
Keeping the Aquarium Between 25- and 27-°C
In order to keep a tropical marine tank between 25- and 27-°C, the aquarist generally relies on both a heater and a chiller. A simple thermometer can be used to manually check the water temperature, but it is even better if the aquarists can control these devices with a controller. An aquarium controller can accurately monitor the aquarium’s temperature and trigger either the heater or the chiller if the water temperature falls or rises outside of a preset range. External controllers are often more reliable than the internal thermostats built into both chillers and heaters. Having said this, many heaters do have easily adjustable and highly accurate internal thermostats.
The Risks of Using a Poor Heater
As with most pieces of marine aquarium equipment, a heater is not a heater is not a heater. There are a wide range of heaters available to the aquarist in terms of quality. Don’t simply go to the big box pet store and buy the cheapest heater rated for your tank size. The result could be a failed thermometer causing your aquarium’s water temperature to plummet - severely damaging or even killing your animals. Alternatively, a faulty circuit on a poorly made heater could cause it to increase the temperature of your aquarium water until your animals are literally cooked. Even if a failed or faulty heater doesn’t kill your livestock outright, fluctuating temperatures cause stress that heightens the animal’s susceptibility to disease.
Heater Ratings--How Much Wattage?
Marine aquarium heaters are generally rated to a certain tank size based on wattage. Using five watts per gallon of tank water is more than sufficient to maintain a stable temperature (some aquarists use half that). In any saltwater tank, it is a good idea to use two heaters. While it is possible to use two heaters rated to half the recommended wattage on each, it is best to have both heaters rated to the aquarium’s size. This way, if one fails, the other will keep the temperature at the desired level.
Submersible or Hang-On
In addition to wattage, the aquarist will need to choose a type of heater. The two best options are either a fully submersible heater or a partially submersible hang-on heater. The hang-on heater generally works fine in a saltwater aquarium system employing a sump with an automatic top off (ATO) device because the water level in the sump does not fluctuate (as long as the ATO is functioning). The submersible heater can simply be placed near the bottom of the sump since, as the name implies, it can be fully submersed. The critical factor is to insure that the heater is never fully exposed to the air.
In a saltwater aquarium system that does not have a sump, the heater will have to go in the tank directly. This is not an ideal situation given that the heater can burn fish if it is left exposed.
The Ideal Heater
An ideal marine aquarium heater will have the following characteristics:
- It will have wattage equal to five watts per gallon of aquarium water.
- It will be fully submersible.
- It will be constructed of thick, shock resistant glass such as the 2mmm Pyrex glass that Jager heaters use.
- It will have an easy to adjust thermostat (although this is less important if the aquarist is going to use an external controller).
- If the aquarist plans to rely on the heaters internal thermostat, that thermostat will be highly accurate.
- It will have a durable, insulated power cord of at least six feet.
