UV Lights

How to have clear water with UV filters


If a pond is having problems with green algae, the best solution is an Ultraviolet light. Water changes, chemicals, stricter feeding, and additional shading all work, but these are only temporary solutions. Most UV lights nowadays involve a special, low pressure mercury vapor lamp. This type of lamp emits UV light around the 264nm frequency, which is the best for disabling the DNA of microorganisms. Ultraviolet sterilization of the water is the only permanent solution that is safe, cost effective, and not dangerous to your Koi’s health.


There are many types of Ultraviolet Lights available. An older type actually hangs above the water and shines down on a stream or a designated part of a filter chamber. These are not recommended because they aren’t very easy to hide and the exposure time to the light usually isn’t long enough to do much good. They are also exposed and exposure to the Ultraviolet radiation could occur.


There are also UV light setups that involve actually putting an array of lamps inside a special filter chamber or even in a stream. These are not recommended for the regular Koi hobbyist too because this type is easily broken. Exposure to the radiation is also a possibility.


The most common, and safe, type of UV light is the one where the actual light itself sits inside a quartz sleeve, which is also in a “contact chamber”. The contact chamber is usually some sort of large radius PVC pipe. Water flows through the contact chamber and the whole unit is self enclosed, which makes Ultraviolet exposure to the skin highly unlikely. This also prevents the quartz sleeve from being easily broken.


Scientists classify Ultraviolet radiation into three types when talking about its effects on living organisms. There is UV-A, UV-B, and UV-C. UV-A, which is in the 380–315 nm range, is the least harmful, but it does cause premature aging of the skin. This is also the range that black lights use to illuminate certain minerals and bowling alleys. UV-B, which is in the 315–280 nm range, is thought to be the primary cause of skin cancer (melanoma). UV-C, which is anything lower than 280 nm, is the deadly germicidal range. This is the type of Ultraviolet radiation that UV sterilizers use. The ozone layer blocks most of the UV-C range radiation from the sun. That is why the depletion of the ozone layer is very, very bad.


Ultraviolet light was discovered in 1801 by a German physicist named Johann Wilhelm Ritter. He used Silver Chloride to prove that there is light before the violet wavelength. Ultraviolet actually means “beyond violet”, ultra being Latin for beyond.


Ultraviolet light is a form of electromagnetic radiation. It disables the DNA (Deoxyribonucleic acid) in living organisms by forcing the bases to join together, instead of joining across the ladder. This prevents any algae or microorganisms from reproducing. Don’t worry, Ultraviolet lights do not leave any residual radiation in the water. Since it originates from a light bulb, the sterilization stops as soon as the light is turned off.


Ultraviolet lights should be plumbed in near the end of a filter system. The water should be as free of suspended waste particles as possible. The Beer-Lambert law states that there is a relationship between the absorption of light and the material that it is traveling through. Therefore, the more waste particles that are in the water at the time of UV exposure, the less effective a UV light will be at sterilizing the water.


When purchasing an ultraviolet light, look for one that has a good exposure chamber. It should be a minimum of two inches wide. For a pond that is larger than 4,000 gallons, look for one with an even wider exposure chamber. Make sure that the inlet and outlet are located near the ends of the unit, for any part of the bulb that doesn’t have water flowing past it is useless. The UV unit should use a quartz sleeve to house the actual lamp itself. Quartz is much more opaque to Ultraviolet light than glass is. UV lights usually have a maximum flow rate. Do not exceed this, utilizing an Ultraviolet light is all about exposure time and not about how much water can be flowed through it. The longer any water is in direct contact with a UV light, the more microorganisms will be disabled.


Ultraviolet light manufacturers usually have different maximum flow rates for disabling algae, bacteria, or small protozoa. Algae removal is the most important and the most economical goal, for it can be destroyed with a much higher flow rate than anything else. In order for a UV light to destroy a bacterium or protozoan, it needs a long exposure time with water in order to be effective. A pond should be “turned over” at least once an hour to be effectively sterilized too. If you have a good sized pond, this would require a large amount of pumps and an even larger array of UV lights.


Ultraviolet lights have become a very common component of filter systems in the last decade. They have made many people very happy by allowing them to easily view their Koi and other pond fish. Ultraviolet sterilizers can even be found on small fish tanks now too.


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