Blog & Latest News from the team at Water Garden Ltd - The importa..
The importance of a Pond UV Clarifer explained

For those of us who own a pond, it’s important to ensure that the equipment used to keep the pond clean & clear is maintained, particularly as we head into the warmer months.  Your UV (‘ultra-violet’) Clarifier is one of the most important parts of your filter system but is often neglected.  Here, Water Garden Ltd discuss these useful pond helpers in a little more detail.

What is a UV Clarifier?

bitron eco self cleaning

A pond UVC is designed to tackle green water.  The green tinge you may have seen in ponds (and later on, a thick green pea-soup) is caused by single-celled microscopic algae which feeds off the nutrient from fish waste and organic detritus within the pond.  Single celled algae cannot be removed simply by passing the pond water through a traditional Pond Filter (i.e. through sponges) as the particles are too tiny to be trapped.  So, a UV Clarifier is used to tackle this issue. 

The unit produces ultraviolet radiation which causes the tiny algae particles to be killed and flocculated (clumped) together.  These much larger clumps of algae are then passed through the filter and become trapped inside the filter sponges.  The UV radiation will also kill off potentially harmful pathogens and microorganisms which could harm fish and other aquatic life.

Why do I need to maintain the UVC?

UV Bulb

The two most important parts within a UV Clarifier are the germicidal bulb  (‘UV Lamp’) and the protective glass shroud (‘Quartz Sleeve’) that surrounds the bulb.  It is vitally important to change the UV bulb on at least a 12-18 month interval as the UV radiation will gradually deteriorate over this period.  So, whilst the bulb may still be glowing blue when looking through the inspection window, the bulb may not be emitting any germicidal benefit whatsoever (in other words, the light is on, but no-one is home!).

bitron eco uv clarifier

The Quartz Sleeve should also be inspected and cleaned when the bulb is due for a change.  A clean sleeve is crucial to allow the UV radiation to pass effectively through and into the passing water flow.  If calcified or covered in dirt, the radiation will be dramatically limited.  A rubber seal (‘O-ring’) is used to seal the Quartz Sleeve to the outer casing and this should also be inspected for dirt deposits and cracks and cleaned or replaced accordingly.  If water breached behind the quartz sleeve, it will likely result in blowing the sensitive electronics in the main controller (the ‘Ballast Unit’) which could mean a new ballast unit is required.

How much UV power do I need in my pond?

Water Garden recommend the following minimum UV wattages, based on whether this is an ornamental pond (i.e. no fish or wildlife), a fish stocked pond (i.e. small hardy breeds such a goldfish and shubunkins) or Koi stocked ponds (i.e. Koi Carp and/or large fish in greater quantities):

Ornamental Ponds:  1 watt per 1,000 litres (220 Gallons)

Fish Ponds:  2 watts per 1,000 litres (220 Gallons)

Koi Ponds:  4 watts per 1,000 litres (220 Gallons)

So as an example, a Koi Pond of 10,000 Litres (2,200 Gallons) would require a minimum of 40 watts of UV power.

What about pumps and flow rates?


A UV Clarifier will need a Pond Pump to pass the flow from the pond to the UVC, then through to a mechanical/biological filter.  As a rough guide, you will need a pump which can pass the entire pond through the UV clarifier at least once every two hours.  On heavily stocked ponds, this could be as much as every one hour or less.  On ponds with no fish, every 4 hours may be fine as there is very little nutrient load in the pond for algae to breed off.

A word on safety.

UV radiation is not only harmful to single celled organisms, but also to humans!  It is very important not to stare at a UV bulb whilst in operation as this could result in ‘arc-eye’ (‘welders flash’) which is a very painful eye condition which feels like having hot sand poured in your eyes for several days – not at all pleasant.  UV radiation can also cause lasting damage to your eyes.  All Oase Ultraviolet Clarifiers and many other reputable manufacturers will fit a safety micro-switch which will cause the unit to switch off automatically when removed from the protective casing, but ALWAYS ensure that the UVC is switched off before dismantling or servicing.

If you need spare parts, UV bulbs, a new Oase UV Clarifier or any advice on how to test and repair your existing one, feel free to call Water Garden Ltd on 02392 373735 or Contact Us via email for expert assistance.

Back to top