Pond Filters
A
pond
filter keeps the
pond clean and safe for your fish and other inhabitants. With an
Ultra Violet Light (UVC) the pond can also be kept clear so that
you can watch what they get up to.
This section has a few different
sub-sections. Click on one of the links below to skip to the part
you are interested in:
Do I
need a pond filter?
How does a pond
filter work?
My water is
still green!
Do I need a pond filter?
Do I need a pond filter?
Lots of people ask us whether
they need a
filter. The answer depends on what you want from
your pond. Ponds in nature often look clean and clear and people
imagine that this is easy to achieve in their garden but there are
actually a few differences.
A natural pond will have a lot
of
plants in it. Plants do two things: they
shade the surface from the sun and they use up nitrates. Sunlight
and nitrates are the two key ingredients for the growth of algae so
more plants usually equals less algae.
Garden ponds tend to have very few plants by comparison with their
natural cousins. Even when we do plant a pond well it starts off
with pots full of compost and very small
plants that are not big enough to use up nitrates
from the pond or shade it from the sun.
Natural ponds have either no fish
or very few fish. These will be the small native varieties like
Sticklebacks which eat the vegetation or insect life in the pond.
This means that they are in balance with the pond’s eco
system. If there are too many fish they’ll deplete the food
and their numbers will reduce.
Garden ponds tend to have many
more fish and all of varieties that get quite big. Even an adult
goldfish can be around 12” in length and weigh several
hundred times more than a Stickleback!
These fish are then fed with high
protein
fish
food (usually
twice a day) in quantities that will make them grow quickly. All of
this food becomes fish waste and is deposited in the water as a
source of ammonia which is very bad for fish health. Bacteria that
live in the pond change the ammonia into nitrite and then nitrate,
which is plant food. As there aren’t enough plants to use up
all the food (nitrates), it feeds the growth of algae instead. The
solution to this problem is a pond filter.
How does a pond filter work?
How does a pond filter work?
Basic
pond
filters act in
two ways, they clean the water of solids and they make it safe for
fish.
Cleaning the water is done
mechanically. The water is pumped into the filter and strained
through the filter media (usually
foams). The solids (muck, sludge, dirt and fish
waste) are left behind on the foams while the clean water passes on
to the next stage. The finer the holes in the foams, the cleaner
the water will be but the more often the filter will need
cleaning.
After a while these
foams will get clogged up and you will need to
take them out and clean them (usually in a bucket of pond water
which is then discarded).
Once the water has been strained,
it goes into the next stage of the filter. This is where the
bacteria come in. Friendly bacteria change the ammonia in the water
into nitrites and then a different type of bacteria turn it into
nitrates, which go back into the pond to feed your plants. The
friendly bacteria are present in the pond naturally but the filter
creates ideal conditions for them to thrive. The filter
contains
bio media, usually
lava rock or bits of chopped up
ribbed
pipe (although
there are many more technical versions too). They have a high
surface area for their size and this is where the bacteria live;
the higher the area the more bacteria can populate it.
My water is still green!
My water is still green!
Basic
pond
filters with
mechanical (foams, brushes) and biological (rock, gravel, chopped
up pipe) media will keep your pond clean for your fish, but
won’t stop it going green on their own.
Ponds go green because they have
suspended algae growing in them. This is the stuff that makes the
pond look like pea soup. It is really just lots of tiny plants that
grow when there is sunlight and nitrates.
A filter on its own won’t
remove the algae; the individual plants are so small they just go
straight through.
The best way to remove the
suspended algae and give you crystal clear water (or ‘gin
clear’ as it is sometimes called) is to add an
ultra violet
clarifier or
UVC. This is basically a tube that the water
passes through. In the center of the tube is another tube made of
quartz glass which protects a UV bulb. The UV light shines through
the quartz glass and into the water. It doesn’t kill the
algae but it does make the little plants clump together (or
flocculate). When the water leaves the UVC and goes in to the pond
filter the lumps of algae are then big enough to be strained out by
the mechanical filtration (foams) and the water will be
clear.
The ultraviolet clarifier causes
no harm to the fish or pond but it can be harmful to bacteria (if
it is strong enough) and so we always suggest that you leave your
UV light turned off for the first couple of weeks when you are
setting up a pond. That way the friendly bacteria colony in your
filter can get established first.
Bearing all of this in mind we
can say that your pond won’t be free of suspended algae
unless you have a filter and an ultra violet clarifier. Often these
are sold as a
combined unit, with the UVC light in the top of the
filter box so that the water is UVed before it goes in to the
filter proper which is underneath. These type of units are easy to
fit (they have fewer connections than stand-alone units), cheaper
to buy than a separate UVC and filter and very effective
Click here for more information
on friendly bacteria and how it works.
Click here to see our range of
pond filters
Now that you know a bit more
about pond filters, why not take a look at one of our other
guides?
Waterfalls
Fountains
Friendly
Bacteria
Box Filters vs. Pressurised
Filters
Connecting the Pond Pump and Pond
Filter
What size of pond pump and filter
do I need to buy?
Filter Maintenance
Adding fish to the
pond
Or click here to see a list of
all our pond building guides
