It is very important to buy an aquarium heater for your fish tank and prepare in case of emergency. Other than a heater, placing a stick-on thermometer on the outside surface of the aquarium is also recommended so that you will know when to switch on or off depending on requirement. Aquarium heater also does not need to be on all the time. Sometimes, a slight drop in few degrees overnight should not affect the fish tremendously but for smaller fish tank, usually 5 – 10 gallons, a temperature drop is much more rapid and thus having an aquarium heater does come in handy.
Certain automatic fish tank heater also comes together with a built-in heat temperature sensor and thus it will automatically adjust itself depending on the temperature of the water. I would recommend this type of setup because a person would not be able to monitor the temperature of the aquarium all the time and thus, an automatic heater is the best option and most suitable to be used for all aquariums.
Before buying an aquarium heater, you must also know the wattage to match it to the size of your aquarium. Generally, a good rule of thumb is to take 5 watts for every gallon of water. For example, if you have a 10-gallon aquarium, you will need at least 50 watts of aquarium heater for it to function properly. Before buying, also check whether the manufacturer has a good reputation and get the best one, which you can afford.