What does a UV sterilizer do?

A UV sterilizer is used to control infections by stopping the spread of microorganisms from one fish/coral/invertebrate to another through the water. It is also used in pond applications to control free-floating algae. When operated correctly, free-floating microorganisms will be killed by the UV light. Note that the organisms must be in the water that flows to the UV sterilizer. The UV light has no residual effect and will not kill organisms attached to fish (e.g., adult stage of ich) or rocks (e.g., algae).

How do UV sterilizers work?

The UV sterilizer utilizes a germicidal fluorescent lamp that produces light at a wavelength of approximately 254 nanometers (2537 Angstroms). The water with the bacteria/algae passes over the bulb (or around the bulb if a quartz sleeve is used) and is irradiated with this wavelength. As the light penetrates the bacteria/algae, it mutates the DNA (genetic material), preventing growth/multiplication of the organism.

What factors influence the effectiveness of UV sterilizers?

Size and type of organism: Theoretically UV radiation can kill viruses, bacteria, algae, and protozoa. In general, larger organisms, such as protozoa, require a higher dose of UV radiation than smaller organisms, such as bacteria. But there are also differences between various organisms of the same type: some bacteria are more resistant to UV radiation than others.

Power of bulb: The amount of UV light produced by the bulb is reflected in the wattage of the bulb. Bulbs with a higher wattage produce more UV light. The ability of the germicidal fluorescent lamp to produce UV light decreases with age, and in most cases, the bulb needs replacement every 6 months. UV light is best produced at temperatures of 104-110ºF; cooler temperatures will result in less output.

UV penetration: If the UV light cannot penetrate the water, it will not be effective. Higher water turbidity will decrease penetration. UV sterilizers should be placed after the biological and mechanical filters so the water is as clear as possible when it enters the sterilizer. Salinity also affects penetration; UV light penetrates freshwater better than saltwater. Finally, cleanliness of the lamp or sleeve is important. If a film or mineral deposit covers the lamp or sleeve, the light will be partially or totally blocked. The distance of the lamp from the water also influences the effectiveness. UV light will only penetrate clear saltwater to a depth of 5mm.

What is the proper maintenance schedule for UV sterilizers?

For most units, the UV bulb will need to be replaced after 9000 working hours of continuous use, however, this time may vary so be sure to follow the manufacturer’s recommendations. When installing or changing a bulb, never look directly at the bulb when the unit is turned on. Doing so can result in permanent damage to your eyes.(The damage can occur without you feeling any discomfort.)

Always disconnect the unit from the electricity when performing maintenance to protect against possible shock. When turned on, the bulb becomes especially hot when in the air and submerging it in water may cause it to break.