For Crystal Clear Sparkling Pond Water - Use Ultra Violet Light Clarifier (UVC)
I call the UV unit as used in a pond environment the Blue Light Miracle Worker.
Clear water as distinct from clean or purified water is obtained by using an
Ultra Violet Clarifier (UV or UVC for short). These pond products have been one of the
best inventions ever for the pond keeper but surprisingly only a very small
percentage of pond keepers around the world know of their existence.
Water that is like pea soup is the result of a vast population of algae feeding
off nutrients in your pond.
Under these circumstances it becomes impossible to see below about 2 cm from the
pond surface. In general the fish do not mind too much but the owner of the fish
Draining the pond and filling with fresh water rectifies the problem only for a
very short space of time - until the algae colonies build up again. Algae
multiply at such a high rate under ideal conditions this means clear water one
day, green water the next day, literally.
Large quantities of dead algae can sink to the bottom of the pond and create
another serious health problem for the fish as the algae decomposes. The message:
about green water is not just an eyesore, it is potentially a deadly serious
situation for the fish in your pond.
What does a UVC do?
Ultra Violet Light Clarifiers in a pond circulating system do only one thing:
THEY KILL SUSPENDED ALGAE and therefore prevent garden pond water
from going green. In killing the algae it also results in the algae clumping
together so that these dead algae can be mechanically filtered out of the water
using the pond filter.
This is what happens ...
Water is pumped from the pond through the UV unit and normally before the water
reaches the biofilter. As the water passes through the quartz tube inside the UV
unit the ultra violet radiation from the lamp (acting like very powerful
sunlight) bombards the algae cells, which are suspended in the water flow. These
algae cells, and only those that are suspended in the water then clump together.
The action of the UV light is to destroy the cell walls of the algae and this
allows the small particles to stick together. If the intensity of the UV is
sufficient to destroy the algae cells more quickly than the rate at which they
are reproducing then the water will not go green. It is as simple as that. This
is why the power (watts) of the unit chosen must be matched to your pond size.
The golden rule of pond keeping also applies here. If you are not sure go one
So efficient is the combination of a good biofilter and a UV that most
suppliers will guarantee crystal clear water when its correctly specified
products are used.
If you have never used UV you will be amazed at the difference it makes to
The UV unit itself ...
What does an UV look like and how do you specify the correct UV?
An UV is an electrical item packaged in a black plastic box, placed inside a
pressurized pond filter or inside a pipe of one form or another. It is piped
(normally 25 mm pipe) into the pumped water circuit before the biofiltration
The product should be boxed or labelled with clear instructions on how to choose
the right size for your pond. You will need to know how much water you have in
your pond. A warning - never submerse the UV unit.
The bigger the pond volume the more powerful the UV must be. The typical sizes
for normal small garden ponds are 4 watts up to 8 watts. For most garden ponds
up to around 4,000 litres 8 watts
is sufficient but read the instructions on the box - if there are no
instructions DO NOT buy it.
If your pond is highly stocked you may need to install a larger UV than you
think, especially in warm sunny climates or where there are high intensity & long sunlight
hours. The reason is quite simple - the more fish the more
waste and therefore the more nutrients for the algae to feed upon.
There is one critical question to ask when selecting any UV. The question is
does this UV have a quartz tube installed? If the answer is no then it is less
safe than it should be and it makes the UV lamp 50% as effective as it should
An 8-watt UV without a quartz tube is only as good as a 4 watt UV with a quartz
tube. Don't let anyone tell you differently. This can easily be proved and has
to do with ensuring the operating temperature of the UV is maintained at around
40 degrees centigrade. If water is in direct contact with the UV lamp then the
temperature cannot possibly be optimised and the efficiency drops dramatically.
At 20 degrees the efficiency is only 50%.
One important maintenance point has to be made. The UV lamp inside the UV unit
has to be replaced after about 8,000 hours use. This is every year at least in
practice. This is a must because the lamp has exhausted its radiation capacity
after this period.
The best time to install a new lamp is early spring. If your pond starts to go
green even if the 1-year is not up it is probably time to replace the lamp in
your UV unit. If your pond remains green after installing a new lamp then remove
the quartz tube and clean it to allow maximum UV intensity through the quartz
tube. It may be a good idea to clean the tube when you replace the lamp anyway
almost certainly it is covered in dead algae, calcium salts and so forth.
You clean the quartz tube by immersing it in dilute acid (even vinegar will do)
for some time before wiping the surfaces clean.
Most people try to control algae by adding chemicals to the pond.
This can create more problems than it resolves and is also a very expensive way
of trying to control green water since chemicals have to be put into the pond
every week. Some of these chemicals are also poisonous in overdose situations
and the fish get killed and also the plants die.
UV can only kill algae that are exposed to its rays. Filamentous algae you
see on the sides of the pond will not be affected. Similarly blanket weed cannot
be controlled using an UV unit.