The Aquazone Ozonizers by Red Sea removes the ugly yellow cast to aquarium water as the ozone purifies and cleans water of harmful bacteria and other pathogens. Utilizes a special high-frequency process instead of electrical discharge to create ozone. Complies with UL 1018 and is maintenance free. Proper dosage levels should not exceed 10 mg. per 25 gallons. Plus model includes Controller. Image shows the Aquazone 200 plus with controller.