Ultraviolet Sterilizers are used as a control to destroy single celled organisms, water borne bacteria, viruses, algae, fungi and protozoa. There are no residual effects when using an Ultraviolet Sterilizer for you pond. Ultraviolet will not affect bacteria life in your filter or lower fish immune systems. The Ultraviolet Lamp emits a germicidal ray which alters or disrupts the DNA or RNA of single celled organisms such as algae, bacteria and protozoa. By properly implementing an Ultraviolet System in-line, these organisms can be eradicated effectively without any harmful residuals. Your Ultraviolet System was made to work as a control for green water and single celled organisms, but the unit will not, nor will any other unit, completely sterilize your pond as the pond itself is not a sterile environment. As a control, this unit will effectively lower your water's bacterial count allowing your fish to stay healthier with less risk of disease and your water crystal clear. Ultraviolet Sterilizers works better on pre-filtered water. We have many different types and brands available. For more information about Ultraviolet Sterilizers, please contact us.