The Red Sea AquaZone Plus Aquarium Ozone Generator/Controllers are the same as the AquaZone Generators, but they have a built-in REDOX meter/controller with a digital readout and user adjustable set point to turn the ozone on and off automatically. Requires ORP electrode, sold separately. Depending on the protein skimmer you are using and the application, you may want to use an air pump. The Air Dryer is included.Features:Automatically controls the flow of ozone according to preset ORPEasy to read back-lit digital displayEasy adjustment of ozone output and desired ORPContinuous display of current ORPSafe and easy to useProduct Manual (pdf format in new window)