The Basics
Ultraviolet radiation destroys living organisms by irreparably damaging the DNA in the cell's nucleus. Simply put, when algae contained in the pond water is exposed to the UV light, it is damaged to the point where the cell cannot divide and reproduce. This genetic damage slowly eliminates harmful algae from the water.
These UV filters are among the slower-working types but they do produce excellent results given enough time. Be prepared to keep manually pulling algae mats out of the water for a while before seeing the results of one's UV filter in the fullest. When those results are realized, they will be significant.
How they Work
A UV pond light is actually very simple. There is a bulb which emits light in the ultraviolet, as well as the visible, spectrums. There is attached to this bulb a quartz sleeve that protects the bulb from the water and a ballast and housing in which the electrical components of the light are contained. There will generally be a spot on the ballast and housing where the light is visible. This is simply to ensure that the bulb is burning. Do not look directly into the light. Even though it is very low power, it's bad for one's eyes to gaze directly into it.
Water is pulled through the pond UV light by the action of the pump. The filter will only be rated to handle a certain amount of gallons per hour (GPH). Exceeding this limit will essentially render the UV light useless. Be certain that the filter one purchases is adequate for one's pond.
There is a bit of inherent confusion where the term "filter" is applied to pond UV accessories. In the proper sense of the word, these are not filters. They do not nor should they be expected to replace a basket filter. They simply kill the algae that comes through them but they remove nothing from the water. One still needs a proper filter to perform this task.
That being said, a UV filter will only clarify water if the water is made cloudy by algae. Any other impurities will be unaffected. However, if one's pond is turbid with algae, a difference will be noticed after one of these filters is kept in use for a time.
A pond UV will not attack filamentous algae. These are the types of pond algae that appear as long, green fans on fixtures such as waterfalls and fountains. These are self-contained colonies of algae and, as such, they won't be dragged under the light. Any algae set floating in the water when these nuisances are manually removed, however, will eventually be passed under the UV bulb and killed.
Making these devices work requires some attention to detail.
Placement
Where filtration is concerned, placement is everything. The filter will be fed by the pump's intake hose. This needs to be located as far as possible from the hose that returns the water to the pond. Having them next to one another causes a water current that essentially stirs the pollutants back into the water. Keep the intake away from features such as waterfalls and fountains, as well.
Maintenance
As a pond UV clarifier or pond UV sterilizer is used, the sleeve will tend to become caked with various types of gunk. This needs to be cleaned. If it is not kept clean, too little UV light will be allowed to penetrate the water and, thus, the algae will not be killed.
SIZES:
8W:POND CAPACITY 6000L MAX FLOW RATE 2400L/H
15W:POND CAPACITY 15000L MAX FLOW RATE 3600L/H
30W:POND CAPACITY 30000L MAX FLOW RATE 8400L/H
55W:POND CAPACITY 55000L MAX FLOW RATE 18000L/H
NB:NOT RECCOMMENDED TO REDUCE OUTLET SIZE