Aquarium UV Sterilization

Ultraviolet sterilization (UV) is a process to eliminate biological contamination, namely parasite fungus and bacteria. Two types are commercially available, both in tube size. Generally the one containing a wet bulb -at which the water passes directly past the UV bulb- is cheaper.

The other type available has a protective quartz tube around the bulb (dry bulb). The latter has the advantage of easier cleaning, since debris and slime will eventually settle on the bulb, or quartz surrounding. Both work on the same principle.

UV sterilization exposes the contaminants with a lethal dose of energy in the form of light. The UV light will alter the DNA of the pathogens, by virtually gluing DNA molecules together. The changed cell structure prevents the organism from reproducing itself (sterilization), therefore eliminating it.

Central multi tank filtration or expensive reef set-ups should consider a UV sterilizer.

The effectiveness of the UV sterilization depends on the exposure time and light/energy intensity. Generally 36’000 microwatts per square cm per second will kill or damage the common pathogens in an aquarium, lower numbers can successfully remove most of them. (1 microwatt is the millionth part of 1 Watt/ 36’000 microwatts would therefore translate to 0.036 Watt)

In general, the effectiveness of the sterilizer is based solely on the flow rate of the water.

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Some considerations:

Hard Water

Hard water will result in mineral build up on the bulb/quartz surface, reducing its effectiveness. These minerals can also protect the pathogens from the energy/light source, allowing them to pass the system unharmed. This effect is also known as shadowing.

Light Bulb

UV lights don’t simply burn out, but will gradually loose their efficiency over time by as much as 60% in one year. The general recommendation is to replace the bulb every 6 month.


Some medications are rendered useless when exposed to UV light, especially antibiotics. UV light should beturned off while medicating the tank.

Food Sources

Some reef critters depend on microscopic organisms as a food source. These organisms grow and reproduce freely but will be destroyed if they pass through the UV sterilizer tube.

Pay Attention

UV light is not only damaging to pathogens in the water but also harmful to the human eye. Avoid any direct or indirect eye contact with the light.

UV Light Close-up

Light is defined by the wavelength expressed in manometers (nm). UV is defined by a wavelength (electromagnetic radiation) from 10 – 400 nm. The natural source of UV light is the sun. A mercury vapor lamp artificially creates UV at different wavelengths as follows:

  • UVA 315 – 400 nm usually found in black light or tanning equipment
  • UVB 280 – 315 nm causes sunburn
  • UVC 200 – 280 nm damaging to exposed cell

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