How long to leave uv light on in aquarium

How long to leave uv light on in aquarium

The use of filters or ultraviolet (UV) reactors in aquariums and ornamental ponds is an old and common technique, yet it is still a subject full of confusion and doubts, mainly about how long they should stay on. UV reactors are very efficient when used correctly and in the required size. The ultraviolet (UV) system transfers electromagnetic energy from a mercury arc lamp to an organism’s genetic material (DNA and RNA).

      It is a straightforward process; UV light acts directly on bacteria, parasites, fungi, algae, viruses, and other hostile pathogens, as long as they are suspended in the aquarium water, exposing them to high-intensity ultraviolet (UV) light.

       To work efficiently, the UV system needs to obey some rules regarding sizing.

       This article will cover everything related to how long the UV light should stay inside your system.

How long to leave the light on

       Generally speaking, the UV lamp should run continuously 24 hours a day for maximum efficiency. The light should only be turned off when introducing drugs or bacteria into the aquarium so that the ultraviolet does not degrade them.

       If you use a UV system to keep your aquarium free of pathogens or algae, turning it off will expose your water to contaminants again, which makes no sense.

       When the UV lamp is on, biofilm and microorganisms usually do not stick to the quartz glove; however, they can stick when the lamp is off. When the light is turned on again, these organisms end up being killed, but they do not come off, thus causing a considerable drop in efficiency, as they do not allow UV radiation to reach the water.

       Some aquarists recommend turning on the lamp occasionally during algae outbreaks or disease; this is not recommended as it can mask some aquarium maintenance issues, leading to future problems.

       Regardless of the problem being tackled, always leave the UV lights on constantly in your aquarium.

How UV light works

       It is a cylindrical tube-shaped container whose core has a UV lamp with some watts scaled to the size of the aquarium or pond. The water sent by a pump circulates inside this tube, which must always pass through a pre-filtration or a filtering system, not to send solid debris that compromises the efficiency of UV radiation.

       The UV sterilizer, better known as a “UV filter,” produces the UVC ray, but it is not a filter, as it does not filter anything, as UV-C radiation does not. This natural radiation is part of the nonvisible spectrum of the sun’s rays around 220 nm (wavelength),

       When UV radiation penetrates the cell wall of an organism, it destroys the cell’s reproductive capacity generated by electrical discharge. It penetrates the genetic material of microorganisms, eliminating their ability to reproduce. UV light can affect the function of living cells by altering the structure of the cells’ nuclear material or DNA. The result is that the organisms die, ridding the aquarium water of these unwanted disturbances.

       It is common to think that UV filters something, even if they sell or call it an ultraviolet filter. UV is not miraculous and cannot remove anything from the system, not even algae or microorganisms killed by UV radiation; it only sterilizes organisms or destroys a series of chemical compounds susceptible to this type of radiation.

       The ultraviolet reactor is just a piece of equipment built to better take advantage of the UV lamp radiation in the water. It does not separate solid particles, microorganisms, or chemical compounds (although ultraviolet radiation can destroy some).

       The UV light will only act on the water that passes through it, not killing algae and other organisms that are not suspended in the water column, such as rocks, substrates, decorations, or fish. As we have already said, the UV reactor only affects its reaction chamber with organisms and chemical compounds dissolved in the water.

       To be effective, UV sterilization must expose the pathological creatures to a high enough light intensity for a long enough period which would be 35,000 to 100,000 microwatts per second per square centimeter as the norm, which resolving gives from 38 to 95 liters per hour per watt or less for units not operating at maximum efficiency.

       These lamps have a shelf life; they last an average of 6 to 10 months. After that, they lose their efficiency, so they must be periodically checked and replaced.

Why use a UV light

       These UV devices can be used in swimming pools, liquid factories (e.g., beer), and aquariums. Some large water purification centers always use some form of UV sterilization. These filters are sometimes used in ponds to help control algae growth, and they do a great job.

       UV for aquariums was a technology developed to quickly and practically eliminate the green algae proliferate in aquariums and ponds and leave the water looking good. However, this light ends up completely sterilizing the portion of water that passes through it, so it can be used to eliminate pathogenic microorganisms present in the water and specific compounds, such as those that leave the water with a characteristic odor or a darker color.


       Contrary to what many people think, UV lighting is not part of the filtering system; it complements it.

       If you choose to use a UV light sterilization system, purchase the correct and specific equipment for the aquarium and research the correct sizing. To have your efficiency pushed to the limit, keep your light on at all times; that way, there will be no gaps from contamination by diseases or algae.

       Always be careful when handling UV lights; the same properties that make it germicidal can also damage human eyes and cause skin cancer or premature aging.

       A UV unit must be placed last in the filtration line when using this system in an aquarium or pond. It does not carry out mechanical filtration but only eliminates the living organisms that pass through it. Never turn on the filter without water passing through it; if it works “dry,” the lamp will burn out.


        Hoffman, G. L. (1974). Disinfection of contaminated water by ultraviolet irradiation, with emphasis on whirling disease (Myxosoma cerebralis) and its effect on fish. Transactions of the American Fisheries Society, 103(3), 541-550.

        Liltved, H., & Cripps, S. J. (1999). Removal of particle‐associated bacteria by prefiltration and ultraviolet irradiation. Aquaculture Research, 30(6), 445-450.

        Pantanella, E., Cardarelli, M., Di Mattia, E., & Colla, G. (2010, March). Aquaponics and food safety: Effects of UV sterilization on total coliforms and lettuce production. In International Conference and Exhibition on Soilless Culture 1062 (pp. 71-76).

        Summerfelt, S. T. (2003). Ozonation and UV irradiation—an introduction and examples of current applications. Aquacultural engineering, 28(1-2), 21-36.           

        Liltved, H., & Landfald, B. (2000). Effects of high intensity light on ultraviolet-irradiated and non-irradiated fish pathogenic bacteria. Water Research, 34(2), 481-486.        

        Becker, J. A., & Speare, D. J. (2004). Ultraviolet light control of horizontal transmission of Loma salmonae. Journal of Fish Diseases, 27(3), 177-180.          

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