Ultraviolet light can be very effective at eliminating viruses, bacteria, algae and fungi. The required UV exposure rate to irradiate common bacteria is 15,000 µWs/cm², whereas the required UV exposure for waterborne algae is 22,000 µWs/cm². Since it is the intensity of light that is doing the sterilizing, we must know how much light energy to use and how much is reaching the target.

Just as some sunglasses and sunscreens reduce UV intensity, so do discolored water, turbidity, dirty quartz sleeves and even some dissolved salts, such as sodium thiosulfate. Lamp temperatures may even reduce output when operated in cold water (110 degrees Fahrenheit/37.8 degrees Celsius gives maximum UV output).

Mechanical and biological filtration does not remove bacteria, protozoa and viruses, so treated water must be disinfected before returning it from your filter system to aquariums or holding tanks.

Ultraviolet radiation (UV) is most effective for its germicidal value in a clear-water application at a wavelength of 265 nanometers. With proper exposure, UV light penetrates a microorganism’s cell wall. It then destroys the nuclear material, causing abrupt modification and quickly bringing about its destruction.

We hear from a lot of people who have UV sterilizers and still experience disease problems. This situation can almost always be traced back to inadequate UV irradiation. Because it is so difficult to measure the intensity of UV energy hitting the water, many buyers have improperly sized their UV sterilization systems. Our team of experts can help you troubleshoot the issues and recommend better disinfectant solutions.

Be aware that some UV lamps age rapidly, and the manufacturer probably states the watts produced when the lamp is new. This wattage can be reduced by as much as 40 percent in as quickly as six months. We suggest oversizing the UV sterilizer by at least 40 percent to ensure you have the sterilizing power required as the lamp ages. We also suggest changing lamps every six months. 

To ensure adequate water disinfection using UV light, first start with clear water, and have a lamp and flow rate that are sized to deliver the correct amount of irradiation for the target organism. If a UV light is flow-rated for 15,000 µWs/cm², and you want 30,000, either double the number of lamps or reduce the flow by half, and so on, for higher dosages.