Trickle Filters (Page 2 of 2)
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The filter holder can be
anything that will hold a stack of bio-balls (or any other filter
media suitable for trickle filters) inside it. The stack of
bio-balls is ideally over 18 inches in height, although the higher
the stack the better. Height matters because it determines how
much surface area the water droplets will travel through from the
time they hit the top bio-balls to the time they've cascaded down to
the bottom ones before returning to the pond. The more surface
area the droplets get in contact with the more nitrates will be
removed from them.
Since bio-ball stacking height
is important in maximizing the 'contact time' of the water droplets
to the bacteria on the bio-ball surfaces, filter holders are usually
in the form of upright towers, hence the name 'trickle towers.' Of
course, any container that looks like a tower (much taller than it
is wide) can be used as a trickle filter media holder. It is
common to see trickle filter made out of used drums.
At the bottom of the filter
holder is the filter exit or pond return, which is usually just a
spout that returns the water to the pond by gravity. Since the
filter media must not be submerged in a trickle filter, it goes
without saying that the entire filter holder must be above the pond
water line. So should the spout be if you want to use it in
agitating the pond surface with the returning water to enhance
aeration.
Thus, another benefit of using
a trickle filter is excellent aeration, not only because of the
exposure of the water to air as it travels down the filter, but also
because of the pond surface agitation that it can provide. By
the way, some hobbyists have their filter exits below the water
surface, using subsurface piping to draw air to the pond bottom,
also to promote aeration. I prefer having the spout above the water
line because I love the sound of splashing water.
Bio-balls are a popular choice
as trickle filter media because they have a high void fraction and a
high surface area-to-volume ratio (something like 160 sq. ft for
every cu. ft. of 1" bio-balls). A high void fraction simply
means that when the bio-balls are stacked, there are large air gaps
in between them that allow excellent oxygenation of their surface
areas. The high surface area of the bio-balls allows them to
contain larger colonies of good aerobic bacteria, as pointed out
earlier. Thus, any filter media that have a high void fraction
and a high surface area can be good alternatives to bio-balls in
trickle towers.
Figure 2. The Bakki
Shower is an advanced type of trickle filter
A trickle filter must be
treated as a biological filter, and not as a mechanical filter.
Debris will not be able to pass through the tiny holes of the spray
bar or drip plate, which will easily get clogged up if the water
they get has some suspended particulates in it. Thus, an
efficient mechanical filter must always come before a trickle tower,
so that the water fed to the latter will already be free of debris.
A well-designed trickle filter
is said to be tens to hundreds of times better than wet filters in
terms of biological filtration efficiency. Koi hobbyists who
have attached trickle towers to their conventional filters attest to
the effectiveness of this accessory in achieving crystal-clear pond
water, even without uv sterilizers. This is why more and
more koi enthusiasts are turning to trickle filters for help
nowadays.
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See also:
Filtration Basics
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