by Ron James, Ph.D.
Reprinted from Koi USA
As there is a multitude of misinformation and misunderstanding regarding the use of a UV system. It is the purpose of this two part article to help clarify the value and functions of ultraviolet light for the average Koi hobbyist.
UV light has two primary uses in fish culture: controlling green water and disinfecting the water supply.
The use of UV for disinfection is not new. Since the 1950's UV disinfection facilities have been implemented throughout the USA, as well as around the world, to disinfect a wide range of water sources; from waste water to aquaculture (fish farming), wherever a greater need to control waterborne pathogens exists. In some instances, without the use of UV, newly introduced pathogens (from infected fish) can create enormous problems which can cause the complete shutdown of a facility, thus creating a great loss of fish. A fish farm is virtually paralyzed and is forced to shut down until some means of disinfection can be found.
What the Koi hobbyist or fish farmer requires is a dependable means of controlling or eradicating the pathogens that are present. UV is a known effective and practical means of attaining this goal. By implementing a UV system, floating algae (green water) and the targeted pathogen can be effectively eradicated or controlled without producing any harmful effects. UV treated water has been proven to be completely safe for fish and humans.
A UV system is only one part of a filter system. A biological filter is a must in keeping Koi. Remember a single bacterium can produced a colony in exces of 25 million within 24 hours. Hence, a biological filter acts like a beehive by producing a swarm of bacteria, which then build colonies scattered throughout the pond, creating bad as well as good bacteria. Consequently, by running pond water through a UV system prior to reentering the pond, you greatly reduce the number of bad bacteria in the pond. While UV disinfection may be useful in preventing reinfection it is not a substitute for antibiotics or other chemotherapeutic agents after infectious or parasitic organisms have attached themselves to the host fish. As UV radiation may affect these methods of treatment the UV system should be turned off during treatment with either antibiotics and/or chemo-therapy.
Unfortunately, most data available from manufacturers is based on research relating either to drinking water or waste water with comparatively few experimental studies done with salt water. Therefore the data derived is based on studies using more powerful equipment. Consequently most WV systems manufactured should only be used as clarifiers to control low strains of algae. All the disinfection research carried out for this article has been done so in fish culture. As the two purposes of using UV radiation (sterilizing and clarifying) are important the industry is plagued by much misinformation, particularly regarding disease prevention and treatment. With Koi enthusiasts, the fear of killing good bacteria is a major concern. Studies have shown, without the use of UV treatment, bacteria will colonize in different areas of a pond and then compete to take it over. There are some people who believe UV treatment will make the water too sterile for any micro-organisms to survive. However, our studies have shown, given the proper UV system, UV treated water provides an excellent well-balanced environment for Koi. Depending on several factors, e.g., fish load, filter system, etc., not all ponds without UV treatment will suffer with bacteria overpopulation. However, the elimination of green water is highly improbable. Many proponents of UV disinfection sometimes overlook the additional benefits relating to ornamental fish; those being that cleaner water reduces the stress on the fish by not having to fight off diseases, thus enhancing its immune system and leading to faster growth and more brilliant colors. It was also noted in some studies that several ponds not using UV had clear water. These ponds were thought be in excellent condition. However, upon testing the water, aromonas were found. This again proves that clear water is not necessarily clean water.
Design Importance:the types of UV lamps and how they work.
Lamps that produce the greatest amounts of UV radiation contain mercury vapor. There are also high and low pressure lamps. The low pressure hot cathode lamp (TS) is the size of a fluorescent and is used most often in clarifiers as it is less expensive.The hot cathode germicidal lamp is similar in its operation to the standard fluorescent lamp as it operates from a ballast and requires a device such as a glow switch starter to preheat the electrodes located at the ends of the lamp. As the life of the electrodes is shortened by frequent starts, continual use (24 hours a day) is recommended. Hot cathode lamps are made from soft quartz, the major drawback of which is that solarization and the blackening of the lamp, decreases the UV output.
The slimline UV lamp is an instant- start lamp available in low, high anti very high intensity. This lamp can also be produced in soft quartz and is often misrepresented as hard quartz. Because of their high initial ultraviolet emission and easy maintenance, slimline lamps are well adapted for sterilization and other applications that require high intensity. This lamp is designed to operate at currents ranging from 120 to 420 milliamperes, depending upon the type of ballast. Use of a higher milliampere ballast increases the lamp's UV output. While the lamp may be energized with a lower milliampere ballast, the lamp may then only be working at half or even less than half of its published rating. Therefore it is very important that the ballast is matched to the lamp. Remember it is not the visable light but the invisable rays that disinfect.
When considering a UV system for disinfection, there are parameters to be set, one of which is identification of the targeted pathogens in order to set the proper dwell time. Each micro-organism has a resistance to UV. The amount of energy required to destroy or disrupt the DNA of the targeted organism is defined in reports on UV dosage. This is commonly measured in microwatts per second of the ultraviolet energy within 254 nanograms.