How does an Ultra Violet Light Clarifier or Sterilizer Work

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Clear water as distinct from clean or purified water is obtained by using an Ultra Violet Clarifier (UV for short).

How does the UV work?

When algae are exposed to UV light the cell wall is destroyed. The result of this is that algae clump together. Prior to clumping a single algae cell has a diameter of about 4 microns (4 millionths of a metre or very very small). Because algae are so small it is difficult for any filter to remove it. However after clumping the filter can do a good job of mechanically removing the algae.

The UV lamp does not prevent algae forming. It works by killing the algae faster than they can make the water go green. The algae will still tend to form so long as the conditions suit them. However if the wattage of the UV clarifier is too low then the water will remain green for the reason that the algae are forming more quickly than they can be killed. If any doubt when choosing an UV clarifier go for a larger size. You cannot overdose with UV!


If you install an UV in a pond whose water is already green then it will take some days to clear depending on wattage of the unit. Also be aware that the quartz tube may well get fouled up with green algae seriously reducing the radiation. If the pond has not cleared inside a week then check the quartz tube and clean it if necessary. Repeat also if necessary. Your pond will go clear unless the wattage is insufficient - promise.


Correctly sized UV & Biofilter combos GUARANTEE crystal clear and clean healthy pond water. Combo units are available from MacArthur Direct  at great prices ... all contain Alfagrog (called Supra in USA)

Buy this Combo filter & UV up to 5,000 gallons ponds capacity

The use of an UV Clarifier in my opinion is absolutely mandatory to be able to enjoy a pond to its maximum and also safeguard fish in a pond from aggressive algae blooms potentially causing fish mortalities. The use of an UV is one of the very best things to happen to pond keeping and has contributed enormously to the growth in successful and enjoyable pond keeping all over the world.

By the way do not let anyone tell you an UV will damage your filter's performance. This is not true. Also pond UV's cannot kill bacteria or viruses as some people claim.

UV will certainly kill bacteria and viruses but not as designed into a pond UV Clarifier. Aquarium units are often designed to control bacteria. They are then called UV Sterilisers, and not UV Clarifiers. There is a big difference.

Breweries and pharmaceutical companies etc use UV sterilisation but the equipment is very expensive and has to be totally reliable.

A final word. If you have not got this blue-light miracle worker then do go out and buy one. You wont regret it.

Ultra Violet Light Clarification
Will Will NOT
Kill any algae exposed directly to the UV rays - ie those algae circulating in the pond water Kill any algae not exposed directly to the UV rays eg Blanketweed, or algae attached to pond surfaces
Do the best job when designed to cope with the system installed Kill bacteria or viruses. The design is such that pond units cannot reach sufficiently high radiation levels. Sterilisation UV units are required for this purpose.
Provide clear water when designed and installed correctly without any doubt so long as murkiness is due to algae presence Normally effect medication so does not have to be switched off during treatment
  Do any harm to plants, fish or filter bacteria

solution to blanketweed problems

For guaranteed crystal clear clean and healthy pond water buy low cost combo biofilters and UV units containing the best biomedia, Alfagrog, by clicking this image Combo filter & UV

"The Complete Pond Solver" by Tony Roocroft

2005 Edition. Essential reading for anybody who wants or has a garden pond. Get 12 Excel pond calculators free as well as "Water Lilies and Pond Aquatics" ebook also free

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