UV sterilizer

Description

A UV sterilizer disinfects water by exposing it to ultraviolet light as it flows through the unit. Both references cited here describe recirculating fish farms, not home aquariums. The Merck Veterinary Manual lists UV sterilization units, along with ozone, as common choices for aquaculturists who want in-line disinfection of system water. According to Merck, UV sterilizers work best at a wavelength of 254 nm and act by disrupting pathogen DNA, and systems that use them usually have a bypass loop that sends part of the total water through the unit. FAO's guide to recirculation aquaculture says the organisms targeted on farms are pathogenic bacteria and one-celled organisms. Merck says a unit has to be designed and rated to deliver a specific "zap dose" aimed at a particular pathogen or group of pathogens, and that, with exceptions, larger and more complex pathogens need a bigger dose to be killed. The FAO guide puts farm numbers on this, in microwatt-seconds per square centimeter: roughly 2,000 to 10,000 to kill 90% of bacteria and viruses, 10,000 to 100,000 for fungi, and 50,000 to 200,000 for small parasites. Neither source translates those figures into a setting for an aquarium. Merck names four things that contribute to how well a unit works: component maintenance, water clarity, wattage, and the flow of water through the sterilizer. The FAO guide adds that UV lamps must work under water to give maximum efficiency, because lamps fitted outside the water have little or no effect once the surface reflects the light. Its maintenance schedule lists, among the jobs for every six to twelve months, cleaning the UV sterilizer and changing the lamps yearly.

Sources

• merckvetmanual.com — https://www.merckvetmanual.com/exotic-and-laboratory-animals/aquaculture/production-methods-in-aquaculture
• fao.org — https://www.fao.org/4/i4626e/i4626e.pdf

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