UV Information - The Truth about UV
Ultraviolet Sterilizers - what you need to know about UV Sterilizers and Clarifiers for Aquariums and Ponds
This page contains important information about using Ultraviolet Sterilization to reduce algae and pathogens in the water in aquariums and ponds.
UV Sterilization is a safe and natural method to reduce waterborne pathogens and algae the causes “Green Water”. UV is as natural as sunlight. Unlike chemical treatments that can potentially harm the fish, beneficial bacteria, and plants in your aquarium or pond, UV does not leave any residuals in the water and therefore cannot harm fish and plants.
A UV sterilizer works in harmony with other essential filters by eliminating nuisance green water caused by waterborne algae that can easily create problems and ultimately reduce filter efficiency.
Protecting Your Pond &Aquarium Fish.
For almost three decades UV sterilization has proven itself as an alternative to harsh copper sulfate chemical treatments to control waterborne pathogens and algae.
The Truth about UV and Ultraviolet Sterilizers!
Regardless of whether you choose to label UV as a water clarifier or a water sterilizer, the same design, performance, and operating principals apply. Successful UV operation means destroying the targeted microorganisms. Here are five main factors that will help determine the ability of a UV sterilizer (or clarifier) to achieve this desired effect.
1. The Lamp Type
There are two types of UV-lamps available: low-pressure or medium/high-pressure. As explained below, low-pressure lamps are much better in aquatic sterilizers.
2. The Lamp’s Length
The length of the lamp being used; also known as ARC length.
3. The Physical Design
The design of the UV's water exposure chamber(body)—the distance the UV has to travel from the surface of the lamp to the inner wall of the UV's body is the primary design criteria that will determine the unit's "UV dose rate" at any given water flow rate.
4. The Condition of the Water
The term used to express the ability of a body of water to be effectively treated by a UV light source is known as percent transmittance. This is a value expressed in percent, which is used to indicate the quality of the water to be treated. The higher the percent transmittance the higher the effectiveness of the UV sterilizer in treating the water.
5. Water Flow Rate
The amount of water that is passed through the UV body will ultimately determine the unit's actual UV dose rate, which is expressed in microwatts per second per square centimeter or (u-watts-sec/cm2).
6. Other Important Factors
Lamp positioning inside the UV body.
Let's start at the beginning ...
UV is an abbreviation for Ultraviolet light, which is a spectrum of light just below the range visible to the human eye. Because UV light cannot be seen by the human eye it is often referred to as UV energy.
UV light is divided into four groups as measured by wavelength: (1) Vacuum UV with wavelengths from 100 to 200 nanometers, (2) UV-C at 200 to 280 nanometers, (3) UV-B at 280 to 315 nanometers, and (4) UV-A at 315 to 400 nanometers.
The UV-C spectrum (200 to 280 nanometers) is the most lethal wavelength for microorganisms, because it disrupts the chemical bonds between the atoms. This range of wavelengths, with 264 nanometers being the peak germicidal wavelength, is known as the Germicidal Spectrum.
When you understand UV light and how it affects microorganisms, you can select the appropriate UV light source and properly design your UV's body around the lamp, or lamps in the case of a multi-lamp unit.
The UV Lamp is the Source of UV-C light.
There are two primary types of UV lamps, low-pressure lamps and medium/high-pressure lamps. Low-pressure lamps produce virtually all of their UV output at a wavelength of 254 nanometers, which is very close to the peak germicidal wavelength of 264 nanometers.
These lamps generally convert up to 40% of their input watts (power) into usable UV-C watts, much higher than other classes of lamps. For example, a 150-watt low-pressure lamp will produce approximately 58-watts of UV-C light.
Low-pressure lamps typically run on low-input power and operate at temperatures between 100º and 200º Fahrenheit. They have a useful life of 8,000 to 12,000 hours, depending on the operating current of the lamp. Low-pressure lamps are the best lamps for aquatic UVs.
Medium/high-pressure lamps produce a very wide range of wavelengths, from 100 nanometers to greater than 700 nanometers, well into the visible light spectrum. These lamps are very poor producers of usable germicidal wavelengths; they generally convert a maximum of 7% of their input watts (power) into usable UV-C watts. For example, a 175-watt medium-pressure lamp will produce approximately 12-watts of UV-C light.
The remaining 163-watts are converted into heat and visible light. Medium/high-pressure lamps typically run on high-input power currents and operate at temperatures between 932º and 1,112º Fahrenheit. They have a useful life of only 1,000 to 2,000 hours, depending on the lamp's operating current.
The length of the lamp being used.
Low-pressure UV lamps come in many different styles and lengths. As a general rule, the longer the lamp, the greater amount of UV the water will receive because it will be exposed to the UV source for a longer period of time.
The physical design of the UV body. This element is completely overlooked by some manufacturers, but is crucial to successful operation.
Key Design Criteria:
- Lamp positioning
Make sure the UV lamp is positioned between the water inlet and outlet ports of the unit's body. Any portion of the UV lamp that is not located between the water ports is rendered useless. Furthermore, when calculating the UV’s performance data, only the ARC length located between the water ports can be applied to the calculation, thus reducing its capabilities.
- Vessel Diameter
Select a unit with the largest diameter body in the wattage you are considering. A unit with a larger diameter will always have a greater contact time. For example, a 25-watt model with a 3" diameter body will flow more water than a 2" body.
- Quartz Sleeve
Make sure the unit you are considering uses a quartz sleeve. The quartz sleeve is needed to isolate the UV lamp from the water to avoid a short circuit path for the lamp's electrical power and to allow the lamp to operate at its optimum temperature by acting as an insulator.
- Water Flow Rates
Do manufacturers list water flow rates at the end of a lamp's life or the beginning? Most UV manufacturers give a water flow rate, but do not indicate whether it applies to a new lamp or one that is at the end of its useful life. Try to find a manufacturer that includes the water flow rate in the unit's end of lamp life rating. The end of lamp life rating takes into account the lamp losing UV-C output due to age and therefore is a more realistic projection of how the unit will perform over time.
Do the manufacturer's water flow rates account for the reduced effectiveness UV light has when treating green water? This information should be listed as some type of percent transmissibility rate or absorption coefficient (decimal value). Units that account for this will have lower water flow rates.
The condition of the water to be treated is also largely overlooked but is one of the most critical in determining the ability of a UV sterilizer to treat the water. Regardless of the type of UV light source used, any body of water with impurities will adsorb UV light/energy.
The impurities of interest are algae, waterborne microorganisms and bacteria, and organic waste. Green water, as water plagued by algae and microorganisms is known, will absorb the UV light emitted by the lamp in proportion to its density (or how green the water is).
The greater the amount of impurities in the water, the greater the reduction in percent transmittance. Percent transmittance is the ability of a body of water to be effectively treated by a UV light source. This value indicates the quality of the water to be treated.
The higher the percent transmittance, the easier the UV sterilizer will be able to treat the water at a given flow rate. A reduction in percent transmittance means the UV will be less effective in dealing with the algae problem. If the UV’s water flow rates have not been calculated with a reduced percent transmittance rate, the unit will have considerable trouble dealing with an algae bloom.
Water Flow Rate through the UV
The basic criteria for a sound UV sterilizer design revolves around a careful selection of lamp type, lamp length, lamp position, and body diameter. These factors, together with the intended water flow rate, percent transmittance of the water to be treated, and UV dose rate needed to destroy the targeted microorganism or pathogen, should be the basis of your decision when purchasing a unit for your pond or aquarium.
All UVs are not created equal!
When researching which type of UV to purchase, remember the criteria laid out in this article, read the manufacturer's literature, ask questions, and most of all ask yourself, does this information provided make sense? If not, consider another UV manufacturer.