How do pond filters work? An explanation of the main types of koi pond filtration.
Pictured below are standard filter systems for koi ponds. The mechanics are quite simple and water flow is shown by the red arrows. A surface skimmer is recommended, although optional, which will remove leaves and surface detritus and can be powered by the same dry pump in each instance. Heating systems can also be incorporated on the return pipework, either using an electric unit or a heat exchanger linked up to a gas or oil boiler. All of the filtration systems are shown hiden under decking which affords the pond owner with a good solid platform upon which to view the koi and pond.
Vortex / multibay gravity fed filtration systems.
The water feeds the primary settlement, in this case a vortex, via a central bottom drain incased in a reinforced concrete base. Once into the vortex the heavy solids are spun from solution using natural cetrifugal forces. From here the water enters a multibay system which typically contain brushes, japanese matting and large aggregate materials which trap particles and provide the bacteria with a surface upon which to perform the nitrification process. The waste from these chambers are simply purge periodically from the system using valves on the base of each chamber. The clean water is drawn from the filter system by a dry mounted pump, passed through a Ultraviolet clarifier to kill algae cells in the water, and out through a mid or top return to the pond. Gravity vortex / multibay filter systems work best when the turnover is at least 60% of the pond volume per hour. An advantage is that the pump can be low pressure and low running cost.
Sieve & Bead filtration systems - semi gravity fed.
The water feeds the sieve, via a central bottom drain incased in a reinforced concrete base. Once in the sieve the water rises and is controlled by a wier which has a float attached to regulate the height. As the water falls inside the sieve it passes through a laser cut stainless steel micron sieve screen. This filters out the fish waste, leaves and particles and allows just mechanically clean water through. The waste from the sieve is simply purged periodically from the system using a valve. From here a dry mounted pump draws the water and pushes it under pressure into the bead filter unit. Within here there are thousands of buoyant 3-4mm plastic beads which float to the top and compact. Here both fine mechanical and biological filtration takes place and the water exits under pressure to the UV unit and then back to the pond by a mid or top return. The bead filter is backwashed periodically in a similar way to a sand filter on a swimming pool, only with the addition of a high volume air blower to agitate the beads to dislodge the waste. Bead filter systems work best when the pump is high pressure and with a turnover of at least 100% of the pond volume per hour.
Sieve & bakkishower filtration systems - semi gravity fed 'Streamflow' pond.
The water feeds the sieve, via a central bottom drain incased in a reinforced concrete base. Once in the sieve the water rises and is controlled by a wier which has a float attached to regulate the height. As the water falls inside the sieve it passes through a laser cut stainless steel micron sieve screen. This filters out the fish waste, leaves and particles and allows just mechanically clean water through. The waste from the sieve is simply purged periodically from the system using a valve. From here a dry mounted pump draws the water the pushes it up over a Bakki Shower filtration unit. This stainless steel unit contains Bacteria House Media (BHM - not shown on the diagram) which provides massive surface area for the bacteria to perform the nitrification process. The pond set up shown is loosely based on a stream flow design where all the water is drawn from one end and replaced at the other. This creates a strong one directional flow for growing koi when coupled with good heat and feeding. The UV is not shown on this diagram as it is recommended that this is used on the skimmer > pump > UV > heat exchanger line to prevent water cooling. Showers are best used at high turnover of at least 150% of the pond volume per hour.
The low budget liner option using a multibay filtration system
If your new pond has to be built on a budget then it is still possible to use a bottom drain and good standard filtration system. In this example below the pond has been constructed using a butyl liner with only block walls. The base has been simply carved from the soil and has sand and a membrane between the exavation and the liner. Using this simple construction method it is possible to build a pond which is both good for koi and your wallet.
The water feeds the filtration system via a central bottom drain incased in reinforced concrete. The water enters a multibay system which typically contain brushes, japanese matting and large aggregate materials which trap particles and provide the bacteria with a surface upon which to perform the nitrification process. The waste from these chambers are simply purge periodically from the system using valves on the base of each chamber. The clean water is drawn from the filter system by a dry mounted pump, passed through a Ultraviolet clarifier to kill algae cells in the water, and out through a mid or top return to the pond. Gravity multibay filter systems work best when the turnover is at least 60% of the pond volume per hour. An advantage is that the pump can be low pressure and low running cost.
