The Milwaukee SMS510 ORP Controller allows you to monitor AND control your aquarium's ORP levels. The unit has a user selectable set point of 0-600 mV and is adjustable with the front panel control knob. Simply plug your Ozone generator into the controllers power plug socket and it will dose until the mV set point is reached. It will automatically switch on again if the ORP falls below the adjusted set point. The unit also has a visual LED Alarm.