Basics:
Ultra violet sterilization is one of the most effective means of controlling algae (green water) in ponds and is also effective at disease prevention in aquariums and ponds and for general water quality control in aquariums and ponds. There is a lot of new evidence as to the benefits of UV sterilization for ALL fish, and many myths have been dispelled such as UV Sterilizers destroying beneficial nitrifying bacteria, so please read on.
UVs are also useful in Reef aquaria, especially new ones where the chance of disease introduction is high and the UVs help in keeping a balanced Redox Potential is useful. As the reef aquaria ages the sterilizer can be placed on a timer or turned on and off as needed.
As for the Redox Potential, this is an often overlooked aspect of both freshwater and saltwater aquarists. The Redox Potential is basically the oxidation and reduction properties of water. This is VERY important for proper breakdown of organic waste!, especially in aquariums where the fish/invertebrates come from waters of low turbidity (African Cichlids) or tend to produce a lot of waste (Goldfish). Most experts agree that the proper Redox Potential should be -300-390 mV (less or more is not good, which is why a proper UV is excellent for this, as this is the range they tend to keep it at).
The key to success is water flow, water temperature and cleanliness of the bulb or quartz sleeve. It is important to have a flow rate that will turn over the pond or aquarium at least once or 1 times per hour for disease prevention or every three hours for green algae control (I have achieved effective disease sterilization as tested with a bacterial cloud with as little as once per two hours with a good installation in an otherwise well maintained aquarium). Example: 100 gph will service a 100 gallon pond well. The reason I mentioned such seemingly slow rates is too high a rate will not usually allow for adequate contact time with uvc radiation. Follow manufacturers recommendations for flow rate [our 15 watt model is 200-350 gph]. The other key is temperature. 60 to 85 degrees [F] has worked best for me.
Quartz sleeves help keep up a higher temperature (around 5 F in my tests) but dont allow for as good of contact with the water and are difficult to keep clean, so in my opinion the benefits are a wash. Which brings me to key # 3, keeping the bulb or quartz sleeve clean? First, you want to change the bulb every 6 months for disease prevention or once every year at the beginning of the growing season for green algae prevention. You want to clean the quartz sleeve at this time too, which is one reason for a simple model without a quartz sleeve, use just throw away the dirty bulb. [Although the temperature aspects of a quartz sleeve are worthy of note].
Back to temperature; if your water is very cold (such as a pond or even well water treatment system), I would suggest pre-heating your water before it passes through your UV Sterilizer unit, this is more effective than a quartz sleeve.
Other factors of note are water turbidity (dissolved waste particulates in the water column, poor circulation (a poor flow pattern that that has the water pickup and return too close where too much water goes unfiltered). If these factors exist you will need a larger UV Sterilizer for an effective pathogen kill.
Many arguments against UV Sterilizers in ponds is that they are not natural, but for the clarity most persons want out of their pond, this is not possible without either UV sterilization or a flow thru stream (although many persons with well planted, well shaded ponds do well with clarity). I also have read many anecdotal aquatic forum and blog posts that state that a UV Sterilizer is not that beneficial to an established aquarium as a healthy aquarium depends on beneficial bacteria typically growing on media in your filter which neutralize ammonia. Unfortunately the problem with this statement is beneficial bacteria belongs in the filter, not in the open water (and there is scientific research to back this up, one just needs to look for better sources of aquarium information and articles). Also this is great for advanced aquarists who are not adding fish and have a healthy Redox Potential, but not in the real world of average and above average aquarists that I have dealt with in the 100s of aquariums I have serviced.
How UVC Works:
All gases, liquids, and solids are made up of elements. The fundamental building blocks of elements are atoms, which in turn are made of electrons, neutrons and protons..., all held together by electronic attraction. This is referred to as polarity, the principle that positive and negative poles attract and remain bound together based upon the strength of that attraction. There are over 100 elements known in our universe. It is the elements that form compounds.
Elements combine to form gases, liquids or solids. For example, water is made of two molecules of hydrogen and one molecule of oxygen. Carbon dioxide is one molecule of carbon and two molecules of oxygen. These and all other combinations of elements are bound together by the force of attraction or polarity at the level of the atoms. Organic compounds. The compounds of our focus are those structures that are organic in nature. Primarily it is the organic molecules that are the basis of indoor contamination. We need to understand these compounds so we know how to clean and purify the home. Organic compounds are carbon based. Life is determined by carbon based DNA and amino acid chains. Carbon is not only found in "life," but a whole range of chemicals. A number of useful organic compounds are made up of carbon, nitrogen, hydrogen, oxygen and traces of other elements. The most recognizable organic compound is based upon the carbon and hydrogen combination, or hydrocarbons. Plastics, petroleum products and gasoline are hydrocarbons. Hydrocarbon Organic compounds tend to break down or decay faster than non-organic. The decaying process means hydrogen and carbon molecules separate. For example, if the plastic (organic) in milk bottle is left in the sun for a couple of years, much of it will decay. Skin, hair, tissue (all organic) decays more rapidly. This also shows the effectiveness in UV Sterilization in removing oil based pollutants from an aquarium
With the understanding that carbon is the building block of life (and more), we now need to look at the forces that will break down organic and carbon based contaminate molecules. In short, a photochemical process, initiated by short-wave ultraviolet can do this. Short-Wave Ultraviolet We all accept but dont understand the damaging effects of x-ray and gamma ray radiation. Why isnt visible light as destructive on human cells or bacteria as x-ray and short wave UV have been shown to be? X-ray, gamma, ultraviolet, infrared and visible light energy all fit in a category called "electromagnetic" energy. They all have the same characteristic "lazy S" energy wave, that travel at the speed of light. The light ray energy is called photons that oscillate, resulting in wave frequency. The difference in each type of wave energy is the wavelength, the distance across this wave. By definition, the shorter the distance across the wave, the more powerful the wave will be. The difference in the wavelength determines how the wave affects its surroundings. It is this wavelength difference that allows short-wave x-ray to pass through walls, while longer-wave visible light cannot pass though the same material; short-wave ultraviolet and x-ray can destroy DNA in living microorganisms and breakdown organic material while visible light will not.
Nanometers: Measuring Light Energy All light energy is measured on a "nanometer" (nm) scale. Nanometer means one-billionth of a meter. The lower end of the scale has the shortest wavelength, and the upper the longest. Cosmic, gamma, x-rays and "C" band UV are all classified short-wave energy. Visible light is at middle ground, at 400-700 NM on the scale. Infrared light is in the upper end of the spectrum, running from about 800 to 1400 NM, and radio waves are longer yet in the 1400 to 2200 NM range. Spectrograph: Charting Light Energy in Nanometers. What is Ultraviolet Light? Ultraviolet light is toward the low end of this scale, from about 100 to 400 NM, with three categories, "A," "B" and "C." UV is beyond the range of visible light and cannot be seen. We only see evidence of its presence. Short-wave UV, called "C" band (100 280 NM) is known as UVC. Most C band radiation is screened from the sun before reaching the earth by the production of ozone in the upper atmosphere. Useful UVC is entirely manmade, found in todays low-pressure UVC lamps. The most effective sterilizing range for UV is within the C bandwidth. This range is called the germicidal bandwidth. The ideal germicidal curve is considered 240 NM to 280 NM, with the most effective at 265 NM. With the initial exposure, UVC has properties that alter the cells of living tissue, particularly microbes. UVC radiation triggers the formation of peptide bonds between certain amino acids in the microbes DNA molecules. This renders bacteria, viruses and molds harmless by robbing them of the ability to reproduce. If the germ cells are exposed for longer periods, they start breaking down to the molecular level (carbon, oxygen, hydrogen, nitrogen ions, etc.).
For further information, please visit ULTRAVIOLET STERILIZATION (How UV sterilization works). This article explains in depth with more links and diagrams the benefits and myths about aquarium and pond uv sterilization.
By Carl Strohmeyer
http://aquariumuvsterilizer.blogspot.com/
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