Saltwater aquariums are almost always stocked with tropical marine life (you can also have cold water marine set ups, but these are relatively uncommon).
This includes marine fish and invertebrates that come from tropical regions of the world where water temperatures are a constant, balmy 77-80°F (25-27°C). This marine life can only tolerate small and gradual changes in water temperature.
This universal characteristic of our favorite marine pets makes temperature (heating and cooling) a super important aspect in any marine aquarium.
The importance of heating is often under-estimated by new marine aquarists, which can lead to heating disasters. The easiest way to wipe out your entire tank results from heater malfunctions, such as a heater being “stuck on” or not heating at all.
The best thing you can do to prevent heating disasters is to buy a quality heater. Cheap, poorly made heaters can and do get stuck on or fail to heat; they can also be a fire risk in your home.
You need to look at your heater as a life support system for your marine life; choosing the cheap and cheerful option can often cost so much more in the long run.
A good heater is fully submersible as opposed to hang on. This is because if the water level drops the hang on model can overheat and burn out.
Another important feature of a quality heater is being made of shatterproof material and is also corrosion resistant.
New titanium heaters are an excellent investment in my opinion, these heaters are accurate, conduct heat brilliantly and usually have a built in temperature sensor which shuts off the unit if it comes into contact with the air which would otherwise cause the heater to overheat and break.
A temperature controller unit is advisable to use with heating and cooling units, this does all the leg work for you and keeps fluctuations to a minimum, which is very good news for marine life. I also advise a thermometer with an audible alarm as an extra measure.
Another good practice is to go for 2 smaller heaters as opposed to one big one; this will make it harder for one to overheat the tank before you realize and if one stops heating the tank temperature wont drop severely.
Remember to handle all heaters with care and set-up as per manufacturers instructions, turn units off when exposing to air or performing maintenance and keep them clean, especially so you can see the indicator light is on. Always plug them into a GFI.
If you live in a hot climate, prefer your home a little warmer or have an intense lighting set-up (such as VHO fluorescent lights for a reef aquarium) chances are you will need an aquarium chiller, which will keep your marine aquarium water below a particular temperature.
This is especially important when you keep corals because the lighting requirements they have cause a lot of heat generation from the bulbs, often times this can cause a water temperature increase of around 7°F!
These lighting set ups can often mean you wont need your heater turned on, however it is advisable to have one as a back up. Once again as the correct temperature is so important it is my advice to purchase a quality chilling unit.
When both a chiller and a heater are hooked up to a temperature controller this is ideal to keep the temperature in your saltwater aquarium constant no matter what else maybe happening and your marine life will love you for it.