First lets begin our discussion with the most basic control method employed by most thermostatically controlled aquarium heaters, ON-OFF CONTROL. On-Off Control is a simple control system in which the heating element is either 100% ON or 100% OFF. The cycling frequency of On and Off is determined by the aquariums temperature deviation from its thermostats setpoint.

PID Control on the other hand is a much more sophisticated temperature control system. In a PID system, the value (or %) of control output is a linear combination of 3 variables; The Error Signal itself (Proportional) + The Error Signals Integral + The Error Signals Derivative. By using this control method a Heating System can provide for the most precise control of your aquariums temperature.