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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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