I have grouped Submersible Aquarium Heaters together with Immersible Aquarium Heaters because of their close similarity.
These are the most common and user friendly of all the heaters, you will find them very easy to setup and install. They are normally in a cylinder or tube shape.
Submersible Aquarium Heaters are just what the name says, completely submersible. Which means the whole heater unit is fully waterproof and operates under the water. Only the power cable comes out of the water.
There is no correct mounting position for these heaters. They can be placed vertically, horizontally or any position in between. Some people say that horizontal is the best mounting position, but I find that as long as there is enough water circulation around the heater you shouldn’t have problems.
Heat rises, so it is also recommended that these heaters are placed near the bottom of the tank to help with the heat distribution.
Good circulation around your heater will mean the heat gets distributed evenly around your fish tank.
Immersible Aquarium Heaters look almost the same as the submersible heaters we just spoke about. The only difference is that they placed into the water, with part of them sticking out which is not water proof. The technology is slightly outdated and the submersible heater is now far more popular.
These heaters normally have markings on them so you can see that you have them at the correct level in the water. It is very important that your water level stays between these markings for the heater to function properly.
There are some common factors between these heaters, like the way they are mounted. The vast majority will come with suction cups which will be pressed up against the glass to hold the heater in position.
Some of the immersible heaters may come with a hanging clip that will clip onto the back glass and hold it in place.
Now you will need to read up on the specifications of any heater you choose, but most good brands will have some sort of cut-off switch built into them. This switch is used to turn the element off in case the heater is turned on when it is not in water.
While these heaters have these safety features I wouldn’t go around testing them out too often. They are there for emergencies or if you make a slight mistake by turning it on. I have had one fail on me before through my own negligence.
Submersible aquarium heaters as well as their immersible counterparts should have an indicator light on them so that you can see whether they are on or not. This again would depend on the type you have purchased, but I would always go for one with a light.
You should keep checking your aquarium Thermometer
and the light on the heater to be sure that the temperature is set right.
A drawback that I find with these heaters is that they can be a bit obtrusive in some situations. The submersible heater is definitely the better of the two types though.
Some people like to have their heaters and other equipment concealed in their aquariums. This can be difficult with these types. It is not recommended that they come into direct contact with things like plants, filters or tank gravel. This can affect heat distribution.
I have also known small fish to become trapped between the heater and the side of the tank. There is normally a small gap left between the suction cups and the glass.
If you keep these factors in mind when you position your heater you should be able to avoid any issues and quite happily use either one of these aquarium heaters.