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pond
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How
to Choose a Pond Filter
 This
page is here to help you make an informed decision when
choosing the right pond filter for your pond.
What is a pond filter?
A pond filter is a container which is filled with material
called media. This media does two or three things:
a) traps small particles of waste matter (Mechanical
filtration)
b) provides a large surface area which is colonised
by a bacterium which consumes waste (Bacteriological filtration)
c) absorbs or converts other toxins which cannot
be trapped or converted by a) or b) above (Chemical filtration).
Most filters are supplied complete when purchased with
a) and b) and the option for c) may be purchased separately.
Fitting a biological filter means that the quality of
pond water is greatly improved. However, it will not guarantee
complete water clarity at all times unless it is used
together with an ultra-violet steriliser.
This combination guarantees crystal clear water. Biological
pond filters must be run 24 hours a day from mid March/April
until end September/mid October (UK Calendar) when they
can be disconnected, stripped and cleaned for the following
Spring season. You will need a pond pump to feed the pond
water to the filter. Make sure to choose the pump with
the correct flow rate for the filter you have chosen.
 Step
1
Calculate the volume of your pond as a pond filter needs
to be matched to the pond volume. To do this multiply
the average length by the average width by the average
depth and multiply the result by 6.23 for gallons. If
you require this in litres multiply the result in gallons
by 4.5.
Step 2
Once the volume has been established check the manufacturer's
recommendations for how many gallons or litres their units
will treat or refer to the Lifeforce detailed product
page which will also supply this information.
Step 3
Decide which type of filter is right for your pond and
its situation and whether or not you will opt for the
combined bio-filter UV option.
NB. For ponds with high fish stocks and Koi ponds, halve
the manufacturer's recommendations for water volume treatments.
 Biological
Filters
Most pond filters are called 'biological' filters because
one of their main functions is to produce the helpful
bacteria as described above. These are either external,
external pressure or internal filters.
External Biological Filters
These consist of a large box which is situated outside
of the pond. Most of them have to have their outlet, (for
water returning from the filter to the pond), positioned
above the maximum water level. This means
that you have to find a way to hide or conceal what can
be a large and unattractive unit.
This can be done with careful planting or stone work.
This type of unit is, however, by far the most efficient
of all the bio-filter options and should be chosen if
at all possible. Top flow filters are available so that
a large part of the bulk of the filter can be buried but
some degree of efficiency is lost with this type. Many
modern biological filters will come with the option of
a fitted ultra-violet steriliser and this option is highly
recommended by Lifeforce. Manufacturers offer varying
degrees of sophistication. Trident Water Garden products
offer perhaps the most comprehensive range whilst OASE
offer sophisticated units of quality construction at a
higher price.
External Pressure Filters
These consist of a container with a clamp down top and
sealing ring. Because the top is sealed they can be positioned
below or at the pond water level. As most of the unit
can be buried they are less obtrusive than the conventional
external filter as above but at the moment choice is limited,
they are more expensive, especially if fitted with a U.V.
and offer treatment for ponds up to around a maximum of
2,000 gallons (9,000 litres). Most are physically quite
small andwhilst this may be an advantage around the smaller
pool, it makes them less efficient. Cyprio-Hozelock are
the current market leaders in this area.
 Internal
Biological Filters
These are usually a small container which is sited inside
the pond and fixes to the intake (suction) side of your
pond pump. Ideal where pond construction or available
space outside the pond mean external filters cannot be
fitted. They are, however, less efficient than external
filters. Perhaps the best of this type is called "Pondworker"
which has a clever modern design and is manufactured by
Interpet.
Maintenance
Biological filters should not be completely stripped and
cleaned during the season if at all possible as this reduces
their efficiency. Foams and other biological media should
be cleaned in a bucket of pond water, not in tap water
as chlorine in tap water will kill the good bacteria.
It is better to clean part of the media at any one time
rather than all of it to minimize disruption to the bacteria.
If the filter does not have a pre-filter section (Where
most of the heavy dirt is trapped) add a layer of filter
matting which can be thrown away as required but will
stop the other media from clogging. A clogged filter will
not work efficiently.
At the start of each season add a powder or liquid filter
start to boost filter operation up to maximum efficiency
as soon as possible. Do not add a filter start if average
water temperature is below 50 Fahrenheit (10 Centigrade).
The filter start additives may also be used on a regular
on-going basis to improve efficiency of the filter. Biological
filters can be stripped and cleaned completely at the
end of the season around mid October (UK calendar).
Vegetable Filters
Biological filters convert the most toxic elements of
decay and fish waste into less harmful compounds.
Two of these, "Nitrates" and "Phosphates"
can build up in the water and create problems such as
water discolouration, algal growth and greater susceptibility
of fish to disease. Chemical filtration can be used
to reduce or remove these compounds but this can be expensive,
especially in the larger pond. Regular partial (Not more
than 10% of total volume) water changes also help. An
alternative is construction of a vegetable filter.
These are usually constructed adjacent to the pond and
consist of a lined area around 10 inches to 15 inches
deep (25 to 38 cm.) filled with gravel. The area of the
filter should be as large as possible. Plant out with
quick growing, heavy Nitrate feeding plants such as Crassula,
Nasturtium Aquaticum and Eleocharis. Water from the biological
filter can be fed through the vegetable filter prior to
returning to pond or alternatively pump fed directly from
the pond.
A great bonus is creation of a bog environment which will
enhance the landscaping of the immediate pond area and
attract a host of wildlife.
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