AQUARIUM HEATER INFO
In almost all cases you will need an aquarium heater to maintain the temperature of your tank. If the temperature of your house gets below the required temperature of the organisms in your aquarium, you will need an aquarium heater.
3-5 watts per gallon is recommended for keeping your aquarium at optimal temperatures
Abnormally cold houses will require more watts per gallon
Using more than one heater is advisable because heaters ultimately will fail one day and having a backup heater will keep your tank temperature from fluctuating wildly in the interim before you can replace your heater.
When changing the temperature of your tank, proceed slowly. Sudden temperature changes stress fish and corals
Fluctuations in temperature may cause stress in your corals and fish