Fish rely on a stable environment to maintain optimum health. Most of your tropical fish require an environment with a temperature between 73 and 82 degrees, which means in most areas of the country, you will need to install an aquarium heater to warm the water and keep the temperature stable. Different varieties of fish require different temperatures and some have lower tolerances for heat fluctuations. Learn the needs of your own fish types prior to heating your aquarium.
Choose an appropriate powered submersible aquarium heater for the number of gallons of water in your fish tank. Check the instructions carefully to ensure the heater is fully submersible.
Examine the heater to ensure the heater casing is intact, the heating element does not show signs of damage and there are no exposed wires.
Find a suitable location in your aquarium and attach the submersible heater using the suction cups provided by the manufacturer. Ensure plants and aquarium decorations do not come in contact with the heater.
Allow the heater to rest in your aquarium for at least 15 to 30 minutes prior to turning it on. This allows the glass casing time to adjust to any temperature change and prevents it from fracturing.
Place your thermometer in your aquarium opposite your submersible heater.
Turn your heater on. Most submersible heaters come with a mark on the control dial indicating the ideal setting; some include a thermostat allowing you to set a specific temperature.
Allow your submersible heater to operate for 24 hours, then check your aquarium temperature. Adjust your thermostat up or down accordingly, and recheck your temperature every four to six hours until your desired temperature is reached.
Add your fish to your aquarium once your temperature is stable and the aquarium water is balanced for your fish.