The Jebao 55W Ultraviolet Sterilizer is used to destroy single celled organisms such as water borne bacteria and viruses. The sterilizer is also used to control algae and and to kill fungi and protozoa. Aqua Ultraviolet Sterilizers are recommended for both fresh and salt water systems as well as ponds. The ultraviolet lamp emits a germicidal ray which alters or disrupts the DNA or RNA of targeted organisms such as algae, bacteria and protozoa. The Aqua ultraviolet sterilizer works better on filtered water. Any debris in the water can inhibit UV transmission. Ideal for outdoor pond, pool, fountain, waterfall, indoor freshwater & saltwater aquarium.