This months featured Hardware article courtesy of:

Ron James, of "Aqua UV"


Ultraviolet Light Sterilizer, Clarifier or Both?

Part 1, Basics

By Ron James, Ph.D.

As there is a multitude of misinformation and misunderstanding regarding the use of UV systems 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 1950s 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), where ever a greater need to control waterborne pathogens (CH2m) exists *1. 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. The fish farm is virtually paralyzed and is forced to shut down until some means of disinfection can be found *2. What the Koi hobbyist or fish farm 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 producd a colony in excess 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 chemo-therapeutic 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 *3. 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 UV systems manufactured should only be used as clarifiers to control low strains of algea. All the disinfection research carried out for this article have been done so in fish culture.

As the two purposes of using UV radiation (sterilizing and clarifying) are considerable 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 over-population. However, the elimination of green water is highly improbable without UV treatment.

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 was found *4. This again proves that clear water is not necessarily clean water.

Design Importance *5, described 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 (T8) 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 being 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 and very high intensity. This lamp can also be produced in soft quartz and is often misrepresented as hard quartz. *6. Because of their high initial ultraviolet emission and easy maintenance, slimline lamps are well adapted for sterilization and other applications that require high intensity *7. (This lamp is designed to operate at currents ranging from 120 - 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 only be working at half or even less than 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; 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.

Pathogen Dosage Reference Aromonas3,620 Normandea Algae Spores15,000 EPA CCV 20,000 Yoshimizu E. Coli 2,600 EPA CCV 20,000 Yoshimizu Saprolegenia Hyphae10,000 Normandea Sarcina Lutea 26,400 Nagy Bacilus Subtilis Spores 22,000 Nagy Ceratomyxa Shasta 30,000 Bedel *Sources *1 Hill 1995, *2 Aqua Ultraviolet 1980, *3 Keller 1977, *4 Aqua Ultraviolet 1994, *5 EPA 1974, *6 Aqua Sense 1980, #7 EPA

Ultraviolet Light: Sterilizer, Clarifier or Both?

Part 2, Energy & Exposure

By Ron James, Ph.D.

The germicidal spectrum on the ultraviolet wave length is 2000 to 3000 angstroms, with a peak of 2537 angstroms (or 254 nanometers). The total UV energy emitted from all sides of the UV lamp is expressed in watts. The total exposure of the liquid is expressed in microwatt-seconds per square centimeter, which is the product of energy, time and area. The same number of microwatt-seconds per square centimeters can be accomplished with a short exposure at a high intensity of UV radiation or a long exposure at a low intensity of UV radiation. Our laboratory and field studies have shown a better 'kill rate' at high intensity, allowing us to increase the water flow rate. Low intensity and slow flow rates caused the quartz sleeves to foul converting our sterilizer into a clarifier. Proteins and nucleic acid, which all microorganisms contain as their main constituents, absorb UV radiation energy. After absorption, the UV destroys or inactivates the DNA, thus preventing the microorganism from reproducing.

Most industrial literature relating to ultraviolet disinfection systems pertains to drinking water. While the sizing charts found in much of the literature accompanying UV equipment are an acceptable standard for disinfecting drinking water and industrial applications, they are often inadequate for fish related pathogens. Often the ballast does not match the lamp and/or the quartz is of a low quality. The value of disinfection rises as the density of the fish population increases. Therefore the UV radiation process is even more important to fish farms and people importing fish to sell. UV irradiation of water in a high density fish culture operation often reduces the transmission of infectious diseases and lowers overall mortality.

In 1994 Aqua Ultraviolet conducted an experiment with juvenile Koi infected with aeromonas bacteria. 20% of the fish in non UV irradiated water died compared to only 1% of those in irradiated water. A similar test was carried by Certified Laboratories on Koi eggs and goldfish with similar results A well designed system is beneficial in the routine maintenance of your pond. UV or ozonation is not an elixir to end all disease problems. It is, however, an excellent source to control disease problems and a sure way to get rid off green water. For one thing, UV does not leave a residual in the water to continue killing pathogens after the water has passed through the sterilizer.

Although Herald et al, suggested in 1970, UV radiation produced peroxy-compounds and other free radicals that could kill some microorganisms, even if the cell had not been exposed to radiation. I feel the percentage of cells destroyed in this way is probably very low and occurs only in the immediate boh Vicinity of the lamp.

One of the most often asked questions "Can I over UV my pond?" The answer is no! A study in over-sizing a 300 gallon pond in the desert, containing 15 twelve inch Koi, exposed to desert sun with temperatures constantly over a hundred degrees, using an 80 watt UV light (designed for 2,200 to 4,400 gallons ) has had perfectly clear water for over 5 years and has had no adverse effect on either the filter or the Koi. You can, however, under-size. Smaller UV units have been put in use as soon as the weather begins to warm up and by midsummer the water started turning green. The reason is that algae can multiply and divide at a much faster rate than the system is capable of handling.

The next question often asked "Can I keep my water clear with plants?" Yes, in some instances, you can. Algae growth is done through photosynthesis. By placing plants in your pond, you can block out some of the sun. However, you also block out the viewing of your Koi. The disinfection of the UV is done through light wave. Hence, many things can refract or inhibit the wave transmissions. Therefore, you should be aware of seasonal turbidity, the size of your pond (by gallons), the surface area, the amount of direct sun upon your pond, water temperatures, the humidity of your area, how many times a day the water in your pond turns over, your fish population and the type of filter incorporated into your system.

Your pond specialist should size your UV for the worst case scenario that your pond will encounter. Note that any chemicals containing copper can foul the quartz sleeve, which can alter the effects of the unit. Clean your unit several times to insure all the copper has been filtered out of your pond. Overall, UV irradiation is clearly preferable to ozonation for the routine disinfection of ponds. UV sterilizers add in the way of reactive chemical species, than ozonators. UV units are easier to maintain, cheaper to operate and require smaller capital investment. Perhaps most importantly, the dosage level of UV radiation can be controlled, whereas, consistent concentrations of Ozone solutions are difficult to substain and can be very dangerous to your fish and yourself. The general rule pertaining to ozone poisoning is "If you can smell it, you're too late to correct it." The level of UV radiation emitted across the surface of the lamp can be measured accurately. There is no reliable method of determining ozone concentration in either fresh water or salt water.

Many industries have been successfully using ultraviolet disinfection for years. Be, however, aware that many UV housings are made of standard PVC. Standard PVC absorbs UV rays, and these units can degrade and become toxic. Some PVC manufactured outside the U.S. contain lead and cannot be used for drinking water in their own countries. Any credible ultraviolet equipment manufacturer should provide service, technical assistance for application sizing and transmission absorption testing. Although I have not described all the benefits of UV irradiation I hope I have clarified some of the misunderstandings and misinformation that is confusing to the Koi hobbyist. Remember these very important words "Recirculating System." After all, that is what your pond has and UV irradiation is one of the great tools that can be used in your system to help keep your pond clean and clear so that you can enjoy your beautiful Koi and pond for years to come.

Editors Note: UV Sterilizers built by Aqua UV are considered "the best in the industry" by most pond owners in the know. Their use of the best materials and high powered, long lasting bulbs has given their sterilizers a reputation that has yet to be met by any other manufacturer. Choose the best Sterilizer for the best performance and avoid the other "Johnny come lately's"!

 Preferred installation of any U. V. light is downstream of the pump. This reduces maintenance , which consists of periodically removing and wiping the quartz sleeves. Turn off power manually or automatically with flow switch (1FM above), when flow is stopped. U. V. lights perform best when the light is left on continuously (except for 2 days, when pond is medicated or treated with bacteria concentrate). To protect eyes, do not look directly into U. V. lights. Replace U.V. lamps after 13 months of use regardless of how it appears to be working (due to solarization of glass, lamp will stop emitting U.V. rays after this amount of time has elapsed). Installation of our LCD hour meter keeps track of lamp operating time, or simply replace lamps every spring. Use our U.V.25W or larger unit to treat your sick or quarantine tank and improve your fish's chances for improvement by eliminating virus, bacteria, and parasites from it's surroundings. Reduction of flow rate through a U.V. light increases it's intensity or exposure to the water. By carefully selecting the properly sized unit and flow rate through it, you can have a clear pond with healthier fish. U.V. Sterilizers greatly improve the performance of ozonation equipment when installed downstream, by reducing the reaction time required.


Ozone has the potential for removing virus and bacteria along with dissolved organic material from pond water. The by-product of this chemical reaction is co2 gas and water. Ozone works well in conjunction with a Ultra Violet Sterilizer.

Ozone, a highly re-active form of oxygen gas, can be generated by either corona discharge or a special ultra-violet lamp surrounded by dry air. Both methods generate ozone best if the air or oxygen makeup is dry, hence a dryer is recommended. The injector creates a vacuum when water is pumped through it. This vacuum is the force which pulls air into the ozonator, and then mixes it and air with the water. The advantage of a corona discharge ozone generator is that it generates more ozone, has no ultra-violet lamps to replace, and is more efficient. Ultra-violet lamps require replacement frequently and thus ultimately cost more.

Any planned use of Ozone should be proceeded by enough study so that you know the potential pitfalls of its use. Excess amounts of Ozone can be toxic to fish and therefore is removed from the pond's water prior to its return to the pond. Removal may be accomplished by a waterfall, stream, carbon filter, air tower, large bio-filter, etc. Obviously, the simplest method of removal is by agitation via a waterfall or stream.


Important Reference and other Neat Stuff!

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