|"Building an effective biomechanical filter is
not tough, making one that is easy to maintain was the
What is the single most important element to a healthy koi
pond? Filtration! What often represents the most work in owning
a koi pond? Filtration! Where do many pond builders cut comers?
It has been said over and over again. The single most
important element of koi keeping is water quality, and water
quality is a product of good waste treatment. Somehow we must
remove the waste products produced in our ponds.
I recently had the opportunity to visit Dr. Ron Malone, an
Associate Professor in the Department of Civil and Environmental
Engineering at Louisiana State University. in Baton Rouge
Over the past 12 years, his team of researchers have invested
over $750,000 in funding from the Louisiana Sea Grant College
Program and the National Coastal Resources Research and
Development Institute, studying biological filtration systems.
They have focused on the development of cost effective water
treatment approaches for use with high density aquaculH ture
production facilities. The result of this effort is a series of
head filters ranging from aquarium size to a unit that can
handle the largest whale exhibits.
Dr. Malone, who leads the project, spent the day with me and
took me step by step through the development and operation of
these new filters. He told me that when he began the prqject 12
years ago, they started working with flooded gravel beds,
similar to what is used widely in our hobby. As they studied the
workings of this type of filter, they saw that the surface area
of the media was not efficiently being used, and that the
systems were very difficult to clean.
In their research, they studied the entire gamut of
filtration media and filter designs. (An interesting story in
it's own right). The goal was to find a media that would provide
a high specific surface area for biofilm development in a small
amount of space (in cubic feet) and to develop a filter design
that would be easy to clean and cost effective.
They found that a spherical plastic bead, approximately 1/8in
diameter (half the size of a pencil eraser), was the media of
choice. The beads they use are made from food grade low density
polyethylene plastic and they float. The beads provide a great
deal of surface area for bacteria growth - about 400 square feet
of surface area for every cubic feet of beads. This compares to
around 100 for typical pea gravel, and 125 for bio-balls. And,
since they are very durable they never have to be replaced.
They discovered that a floating bead worked particularly
well, since the beads would pack into a static bed at the top of
a filter chamber, providing the pockets to trap particles and
grow bactena, much like an under gravel filter in an aquarium.
Then, when the filter requires cleaning, they turn off the
pump and agitate the beads to break free the solids. The solids
are then flushed out the bottom of the filter. In their
commercial designs, called prop wash systems, they used a large
chamber capable of holding 6 to 200 cubic feet of beads.
units are cleaned by a powerful propeller system which
intermittently agitates the beads within the filter, shearing
off excessive biofloc (loose bacterial colonies) and releasing
captured solids. When the propellers are stopped, the beads
float to re-form the filtration bed while the solids settle in
an internal settling cone forming a thick sludge. The sludge is
removed from a drain at the bottom of the cone. Only sludge is
removed so the water loss associated with the cleaning process