An apparatus and method for modifying viruses and bacteria in a closed loop system that irradiates the fluid multiple times through the same channel. The apparatus consists of a cuvette, an irradiation station, a peristaltic pump, and a bottle. A plurality of power control switches controls the operation of the apparatus. This includes an on/off power switch, an on/off pump control, and a ultraviolet light control switch. A timer is provided to regulate the time period the cuvette is exposed to the ultraviolet radiation within the irradiation station. A cover is provided to enable the cuvette to be used and exposed to ultraviolet radiation within an enclosed environment.