Do UV Sterilizers Hurt Fish?

An ultraviolet sterilizer promotes fish health and aesthetic beauty by irradiating harmful microorganisms. Because the irradiation happens in an enclosed chamber, the risk to aquarium inhabitants and the aquarist is very low. The benefits, however, include effectively managing many water-born pathogens and other microorganisms that can harm your fish and cloud your water. While not effective by itself for filtration, a UV sterilizer can be a safe and affordable piece of equipment to safeguarde your aquarium.

  1. Safety of Aquarium UV Sterilization

    • UV sterilization is commonly used in food, air and non-aquarium water purification systems and is widely viewed as safe and effective. While prolonged exposure to UV light can be dangerous to people and animals kept in an aquarium, a properly installed UV sterilizer shields the UV light and poses little risk to either the aquarist or the fishes and other animals in the aquarium. Many UV sterilizers are EPA-registered.

    Why a UV Sterilizer is Safe and Effective

    • Most aquarium UV sterilizers use a specialized fluorescent lamp in a quartz sleeve to create UV light at a sufficiently short wavelength to irradiate microorganisms in aquarium water inside the sterilizer. When used properly, the irradiation will safely and effectively kill many pathogens or limit their ability to reproduce. This can greatly reduce the risk of disease outbreaks, while at the same time neutralizing free-floating algae cells and creating clearer aquarium water.

      Bulb wattage and dwell time -- the amount of time water remains in the sterilizer -- are critical factors in determining the effectiveness of a given UV sterilizer. Dwell time is controlled by flow rate and usually measured in gallons per hour. A lower flow rate will allow a lower watt bulb to control algae, bacteria and parasites, but it will take longer to treat your aquarium water, especially in a large system, where a higher watt bulb is generally necessary for the increased flow rates. Regardless of wattage, when properly installed, the UV light is entirely shielded within the sterilizer.

    Types of Aquarium UV Sterilizers

    • There are two main types of aquarium UV sterilizers: inline UV sterilizers and hang-on-the-back (HOB) UV sterilizers. Both are safe for use with a home aquarium if installed properly. Inline UV sterilizers are usually incorporated into a remote, sump-based filtration system with some or all of the filtered aquarium water passing through the UV stabilizer before returning to the aquarium. HOB UV sterilizers generally hang on the back of the aquarium, where water is pumped directly into them from the aquarium and then returned to the aquarium after sterilization. In most cases, inline UV sterilizers are appropriate for larger systems, while HOB UV sterilizers work well on smaller systems.

    Maximizing Effectiveness

    • A UV sterilizer should be matched to the size of the system and the desired outcomes in order to work effectively. Lower wattage bulbs at low flow rates may be effective at controlling algae but may be ineffective at controlling parasites. To maximize the effectiveness of a UV sterilizer, the proper sized bulb must be used with the manufacturer recommended flow rate. Because flow rate is often dictated by aquarium size, the larger the aquarium, the higher the wattage of the bulb. As such, a 75-gallon system will usually require a higher wattage bulb than a 20-gallon system.

    Safety for Your Fishes

    • A UV sterilizer is not a one-stop shop for aquarium filtration or avoiding disease outbreaks. In order to keep your fishes safe and healthy, the aquarist should use a UV sterilizer in conjunction with other filtration methods and good husbandry. Like any piece of equipment, a UV sterilizer must be maintained per the manufacturer's instructions, and it should be turned off when certain medications are being dosed in the aquarium.