How to Choose an UVC (Ultra Violet Clarifier) for a Fish Pond

If you want a crystal clear pond, and who doesn't? Then the ultimate solution which works 100% of the time if the UV unit is correctly sized is to incorporate an UV clarifier (ultra violet light clarifier) into the pond water circulating system.

Almost All Fish Ponds Go Green and Murky in Summer ... Except Those That Have an UVC Installed

In a well stocked fish pond you will need to install a system that will make sure that suspended algae that cause murky pond water are killed. Algae will form in all ponds and that's why all fish ponds need some form of algae control. An alternative to an UV clarifier is Viresco.  A correctly sized UVC and Viresco in combination will work miracles in your pond as far as water clarity is concerned. Remember no UV Clarifier will resolve a blanketweed problem whereas Viresco will and that's why using a combination of Viresco and an UVC is suggested.

Algae are tiny plants and they thrive on sunlight, warm weather and high nutrient levels in water. The symptom of high concentrations are cloudy water ... often green pea soup-like or brown. You will not normally be able to see your fish during the day because the algae floats to the pond surface to catch as much sunlight as possible.

The fish in general do not mind the algae although if things get really our of control the excess algae can remove all oxygen from pond water and under this circumstance the fish will die from suffocation.

Ponds that are green in summer often clear in winter because the algae grow so much more slowly in the cold water. But when spring arrives and water warms up then the murky water re-appears too.

How to Specify the UVC

If you buy a filter then go for one with an UVC included. Always remember the UV light source must be replaced every 8000 hours or so (ie 1 year of full time use). The light source has been depleted of its UV radiation power after this period of time.

The table below is a good indication of the wattage (an UVC is specified in terms of wattage of power used to generate the ultra violet light) required to treat the volume of water in the ponds shown. The greater the wattage then the greater the amount of algae infested water that can be treated. This is correlated to pond volume and sunlight.

If you have extra fish and/or extra sunlight and/or extra high water temperatures then you may have to go for a bigger unit than this table suggests.

The UVC is normally installed in line just before the filter.

Table of sizes, pond volumes flow rates

The specifications below are on the conservative side to take into account the high sunlight conditions and warm water conditions in South Africa. As a result they may vary from what you see in retail outlets. It is far far better to get an oversized UVC than one on the borderline of effectiveness. You will see from the table that there are 2 types of UVC's with the same wattage. One is referred to as the Professional range and is best suited to heavily stocked ponds. The normal UVC is best suited to ponds not overstocked with fish and ponds which see light fish feeding. The Professional UVC units come with a quartz tube installed thereby increasing efficiency of the UV lamp (the lamp is insulated from direct water contact and thus performs at higher temperature and with higher UV radiation efficiency).

Normal UVC Clarifier Model Wattage (No Quartz Tube)	Pond Size in Litres
8	6,000
15	12,000
30	20,000
55	40,000
Professional UVC Clarifier Model Wattage (includes Quartz Tube)	Pond Size in Litres
8	6,000
15	12,000
18	10,000
30	20,000
36	24,000
55	40,000
The amount of UVC wattage required is a function of: fish stock density, water temperature, quantity of food fed and sunlight exposure. Each pond is different therefore. If in any doubt go one size larger.

Important note: No UVC will eliminate blanketweed. An UV clarifier can only kill algae that are pumped through the UV clarifier unit. If you have a blanketweed problem then the only really good solution is to use Viresco.