A quality heater is necessary if you intend to maintain a successful tropical freshwater, marine fish or reef system. Temperature fluctuations often go unnoticed by aquarists and can cause stress to fish and corals.
Most heaters include a built-in thermostat to select the optimal temperature for your aquarium, however, the use of a thermometer to monitor the temperature is highly recommended. You might consider a temperature controller for keeping a stable environment in your aquarium since they offer more precise readings and an advanced feature set.
A minimum of 1-2 watts per Litresis recommended to keep aquarium temperatures at an optimal level. Aquarists with larger tanks should consider using more than one heater. In the unlikely event that your heater goes, have multiple heaters in place safeguards your tank from crashing