BIOLOGICAL POND FILTER OR BIOFILTER
A filter box is essential for cleaning
your pond water. To ensure your filter is functioning to its maximum
capacity it must run for 24 hours a day, and be connected to a pump
of the right size for your pond.
It is a myth that a filter works by removing physical dirt and this
keeps the pond water sparkling clean. Sadly this is not true, although
a small amount of waste will be strained from the pond as it passes
through the filter. The most important purpose of the filter is to act
as a mini sewage system for the pond. In simple terms the media within
the filter creates a huge surface area, which becomes home to many millions
of helpful bacteria. When fish waste, excess food or decaying organic
material fall to the bottom of the pond it starts to break down and
release toxins into the water. As the water passes through the filter
the helpful bacteria break down these invisible toxins and any other
organic waste which get caught up in the filter. Clear water does not
mean healthy water.
Therefore it is essential to buy a filter, which can easily cope with
your pond volume and garden fish stock. You need to know the volume
of your pond to 80% accuracy if possible. Also consider that your garden
fish will grow, and as they do they will produce more waste, so always
opt to buy a filter that is bigger than required. If you are intending
on keeping a large koi pond, it is better to purchase a combined UV
and filter for cost purposes.
Size of filter required
Goldfish - the volume of pond water should be filtered every 2 hours.
Koi - the volume of pond water should be filtered every hour.
and Filter Sets
These pump and filter sets work out cheaper than if you had bought a
filter and pump separately. You can also guarantee they are compatible
as they will be have been made by the same manufacturer.
All in One Systems
This consists of a pump, filter and UVC unit. It is very easy to install
and all of the equipment is hidden under the water.
types of biological filters
Gravity Return Filters.
These filters are pump fed with gravity outlet. These will require a
pump in the pond that feeds the filter. Water will then simply pass
through the filter and return to the pond under gravity. This means
the filter outlet must be higher than the point at which you want the
water to return.
Pressure Filters are ideal for small to medium size ponds and are directly
fed from a pump in the pond. However since the filter is a sealed unit
the water is still under pressure when leaving the filter, allowing
much more flexibility in the positioning of the unit.
Gravity Fed Filters are ideal for larger Koi ponds. They are complex
units to install and expert advice is required.
It is impossible to have a filter too big
for a pond and Koi ponds should have the biggest filters of all.
A pond UV clarifier is an electrical unit which water is pumped through
before it reaches the pond filter. Its purpose is to kill algae cells
by attacking them with UV rays, causing them to clump together therefore
making it easier to remove either by your filter or pond vacuum if you
have one. A UV clarifier only works in conjunction with your ponds biological
The purpose of the UV clarifier is to control the build up of algae
in the pond. Other methods of controlling algae include introducing
pond plants, building your pond in a shaded area or using pond algaecides.
Pond algaecides are not a wise choice if you have garden fish in your
pond as they can be potentially dangerous to the fish. Therefore the
best method to avoid green water permanently is to use a UV clarifier.
Using this process holds several advantages including easy installation,
it doesn’t interfere with the chemistry of the water and it causes
minimal stress to your garden fish.
Algae have some beneficial uses to your garden fish as it is a valuable
source of nutrients particularly to recently hatched fry. However, green
water which is caused by floating algae bloom stops you from being able
to see your garden fish which could have disastrous consequences if
there are sick or injured fish in your pond as they can not be seen
properly. Also at night time algae respires causing the levels of carbon
dioxide to rise along with the waters pH level. Such variations in water
quality cause your garden fish to suffer with stress. The fish in the
pond will have to compete with the algae for oxygen and can cause fish
The combination of using a filter which
removes toxic ammonia and nitrates from waste and the ultra violet clarifiying
process is very effective and maintains a beautifully clear sparkling
pond which your garden fish will flourish in.
Using a UV clarifier will cost less money in the long term not to mention
time and effort in controlling algae.
Considerations when choosing a UV clarifier
for your pond
- It is impossible to have an UV clarifier
too big for your pond.
- If your pond is shallow, pick a larger
- If your pond is exposed to full sun
with no plants, again pick a larger unit.
- Ensure the unit can cope with your
desired flow rate.
Consider purchasing a combined biological
filter/UV clarifier system. You will need to ensure that BOTH functions
are compatible to your ponds needs. A combined unit is simpler to install
than separate units and has less plumbing.
The section on pond
maintenance explains what checks should be carried out
on your pond pump and filter throughout the year.