How To Choose a Pond UV Clarifier

Choosing an Ultra-Violet Clarifier (UVC)
The water in newly filled ponds normally turns green after about fourteen days. There are three ways to remedy this, the first involves endless patience and a lot of pond plants, the second means using chemicals and the third is simply to fit a pond uv or ultra violet clarifier.

How a Pond UV works
Most ultra violet clarifier (UVC) consists of a UV tube seperated from the water by a quartz jacket. Water passing through this jacket is exposed to ultra-violet light emmitted by the tube. The light damages and disrupts the cells of algae, causing them to clump together and die. These large clumps of algae can then be removed from the water by a pond filter.
What Size UV?

Well-filtered ponds will always have a good growth of algae. So called "green water algae" are primitive plants that thrive on warmth, light and nutrients. During the spring and summer these conditions are met in Koi ponds to a far greater degree than in ponds that are heavily planted, and whose surfaces are shaded from the sun by the leaves of water lilies. Koi ponds tend, with a few exceptions, to be rather bare environments in order for fish to be properly appreciated, water clarity is a prerequisite. Unfortunately, these types of shade-free ponds receiving direct sunlight can warm up and turn the colour of pea soup virtually overnight. These factors make it necessary to study the manufacturers recommendations as to the volume of water their uv units will treat very carefully. Koi ponds will require UV units two to four times larger than well planted goldfish ponds. Below is a chart giving a guide to selecting a UV with a typical double ended tube.

UV Chart

UV Chart

Stand alone UV's
Pond uv clarifiers should always be used in conjunction with a pond filter and I would normally recommend that you buy your filter with a suitably sized pond UV incorporated. However there are circumstances where a stand alone UV would be beneficial. As fish grow they produce more waste which will put added burden on your original pond UV, you may have been tempted to add extra fish, this also increases the need to for additional UV clarification. Koi keepers who have built bespoke pond filters will also require stand alone UV's. For the Koi Keeper building his own filter we highly recommend Kockney Koi's Yamitsu Algae Master VC. They come with hose tails for connection to flexible hose but can also be plumped straight into rigid pipe.

Life of UV Tube
The power of pond uv clarifier tubes fades over time reducing the units ability to eliminate green water. This makes it important to change the uv tube regularly. PLS tubes (single ended) should be replaced annually whilst standard double ended uv tubes need replacing every six months.

Cleaning the UV Quartz Sleeve
Most pond uv units have a quartz glass tube that separates the uv's tube from the water. Over time dirt and calcium deposits build up on this quartz sleeve reducing the units effectiveness, so it is a good idea to clean these annually. Be very careful as quartz becomes brittle over time and it is easy to damage the sleeve when removing it from the unit.

Siting a Pond UV
The water flowing through a pond uv should be forced through the unit under pressure. In a pump fed system this means the UV will be situated after the pump but before the pond filter. In a gravity fed filtration systems the pump is placed after the filter and the pond uv after the pump.

Chemicals versus Pond UV
Chemical remedies (mild herbicides) were and still are a recognised remedy, but they can be expensive to administer and you have to use them repeatedly. This type of treatment can also retard the growth of higher growing plants. Pond uv's will not affect plants.