The principles behind the models developed to show several variations on building a Koi pond and filtration systems are to demonstrate that with a little
thought and planning, massive energy savings and hence running costs on a Koi pond can be minimized.
When the running costs of a Koi pond over a few years are taken into consideration they can easily dwarf the total capital costs of the Koi pond in the first
place. That said, there is no such thing as a cheap Koi pond. You should naturally be suspicious of Koi pond building quotes that are significantly cheaper
than the norm, or which include pressurized filtration systems such as sand filters and pressurized bio-filters.
It is up to the Koi pond owner/builder to ensure that
a) Maximum efficiency is extracted from every energy rand/dollar spent
b) Minimum effort is exerted by you as the owner in maintaining your Koi pond. You should not become a slave to your filtration system!
c) That the building of your Koi pond is done properly the first time. Koi ponds have a life span of at least twenty years during which you do not want
to see cracks developing, leaks springing up and filtration systems accumulating a lifetime of debris
The systems shown in these models have been developed to show how low pressure, high efficiency systems that require minimal maintenance can be
achieved with some careful planning.
The models are detailed and you should not assume that the positioning of pipes is accidental. The notes attached to the diagram are an integral part of the
model and you should read them carefully and understand their implications fully in order to ensure your own Koi pond success. No two Koi ponds are ever
the same and the important principles that are outlined in the model and in the notes are what should guide you. When you need help in our design we are on
hand to offer advice.
Surface skimmers have NOT been included in the 3d models. Surface skimmers are vital pieces of equipment in Koi ponds but they are typically pump
driven and comprise a separate water circuit all on their own in Koi ponds. In some cases skimmers can be coupled directly to filtration water pumps as in
the case of pump fed gravity return based filtration. What is important to note is that skimmers should be considered as separate circuits for now (with their
possible integration to be included later on in the design).
Filtration is considered in two separate stages. First comes mechanical filtration followed by biological filtration. In all instance the filter chambers are fed
via a Settlement Chamber which is a primary separator of larger mechanical solids from the water stream that then feeds the filters. In essence the settlement
chamber acts as a rough first stage mechanical separator of solid material.
The mechanical filtration that follows then targets the smaller particles and separates them out from the water stream. Mechanically clean water is then fed
into the biological filters which then remove the dissolved toxins from the water (primarily ammonia produced by the Koi themselves).
This 3d model makes use of a pre manufactured fiberglass pond that we have installed at our premises. The airlift model included in this set of 3d models is
in fact an accurate model of the exact system we have up and running, which you are more than welcome to come and see for yourself at our premises in
This 3D model is to scale! So the dimensions on the units are exact and you can duplicate the airlift system on your Koi pond exactly the same way we have
done ours here. We can attest that the system works – and it works brilliantly. The savings speak for themselves.
The pond has a capacity of approximately 12 000 litres and being pre-manufactured allows a significant advantage in that leaks and sealing of the Koi pond
are not a problem. The pond in question however is not necessarily relevant to the concepts being outlined in the filter model – you can adapt the filters to fit
any size or shape Koi pond.
We have attempted to show as many different variations on a theme within these 3 models as possible. These variations are detailed in the notes. If you see
what looks like a discrepancy, it might well be (in which case send us an e-mail or drop us a line), or it might be deliberate to illustrate a point. When in
doubt consult the notes below.
Gravity Fed Pump Return Filter Systems on Koi ponds
In this environment the idea is to use gravity to fill your filtration system. You then use a pump to empty the filters (which are then replenished by the
gravity flow of water from the pond).
1. The water being returned to the Koi pond is under pressure from the pump. It can be pumped to a water feature such as a water fall.
2. The water being returned to the Koi pond can be used to create additional water movement and circulation in the pond with more pressure than
with a gravity return.
3. If the pump is located close to the pond, the efficiency of the pump can be maximized by shortening the length of pipe through which the pump
must return water back to the pond. Note that piping efficiencies apply to both suction and discharge lines!
4. A bead filter can be incorporated as shown to act as a final stage water polisher. In this scenario the load on the bead filter should be light.
1. Matching water supply to pump capacity needs to be done carefully using large bore piping connecting the filter chambers together. If the piping is
unable to deliver sufficient water to match the pump then the pump will run dry and your bill for new water pumps will become significant.
Note that typically a pump can be used to drive surface skimmers and hence also deliver a pressurized water return to the Koi pond.
Notes to 3D diagram.
Gravity Fed Pump Return Filtration Systems
In these systems you need to ensure adequate flow to the filters such that your pump doesn't drain them faster than gravity can refill them. Large diameter
piping or appropriately constructed chambers are the order of the day here! Pumps that run dry or worse, suck small quantities of air can cause significant
damage to your Koi via the dreaded gas bubble disease.
You can clearly see the feed to the settlement chamber via 2 x 110mm pipes running from the bottom of the Koi pond. It is a good rule of thumb to rather
put more bottom drains into a Koi pond than fewer since these are not something that can easily be added after the pond has been built. Generally use one
bottom drain for the first 10 000 litres and one per 15 000 litres thereafter.
In the case outline we have run two bottom drains. This is to ensure that the settlement chamber is always filled as close to possible to the Koi pond water
level when the system is running but a single drain on this size pond would be sufficient.
What is important to note is that there is a measure of the pipe standing proud of the sloped floor of the settlement chamber. This protruding piece of pipe is
extremely important because this is what you will be placing your stand pipes onto when you are performing your filter maintenance. In other words, do not
cut this pipe flush with the bottom of the settlement chamber!
Stand pipes are important to be able to isolate your Koi pond from the filtration system. Without them you would not be able to drain your settlement
chamber with the Koi pond filling it up.
The depth of the water from the surface level to the protruding pipe is important and should never be less than 400mm. If your settlement chamber is some
distance from your Koi pond this should be increased to 500 or 600mm.
This number is important because it determines how much 'pressure' your Koi pond can exert on the pipe when you pull off your stand pipe. The more
pressure the better because this will 'flush' accumulated debris that has settled within your bottom drain pipes out and into the settlement chamber form
which it can be removed. Failure to do this will allow for debris to slowly solidify in your bottom drain pipes until such stage as they clog up entirely, which
is clearly going to present a massive problem for you in time.
This is a 110mm pipe that is used to feed the first stage of the filtration system, the mechanical filter. It is a good idea to extend this pipe into the chamber
itself and slot it with an angle grinder. This will prevent large debris such as leaves from making their way through to your mechanical filter. Note that this
feeds into the bottom of the mechanical filter.
The mechanical filter is filled with a floating media. As the water from the settlement chamber progresses up through this bed of media the fine solid
particles become entrapped within the bed.
In this case this is a second spare 50mm drawoff line. As you will see it is used in the airlift model to feed the U/V line.
This is a spare 50mm drawoff line. It may not necessarily be used but install one just in case anyway. The cost is minimal and if you need it later on you
have access to it. If you are thinking way ahead it is not a bad idea to make this 110mm (which you can then reduce later on if you need to).
This is the exit pipe from the mechanical filter. It is a 110mm slotted pipe line that allows mechanically cleaned water to pass through to the biological filter
chamber. The pipe is slotted to prevent the media used with in the mechanical stage from escaping across to the biological stage. You need to ensure that
there are sufficient slots to exceed the water flow rate drawn by the pump of course. You will note that there is an identical pipe on the exit stage of the
biological filter for precisely the same reasons (bio media tends to clog pump impellers efficiently).
6. & 7.
These are 20mm airlines plumbed into the filters. For those familiar with our systems both stages are filled with the same media – it is a small plastic wheel
that is designed top optimize the bacterial colonization of the media.
The biological stage has air continually running through it via the 20mm line detailed as 7. There are 2mm holes drilled on the underside in the horizontal
section closest to the bottom of the tank which allows for largish air bubbles to generate a turbulent moving bed environment within the filter. This causes
the media to move chaotically within the filter chamber. This movement improves the efficiency of the media massively allowing for a far higher
performance than traditional static media.
The airline 6. is used to backwash the mechanical filter. Air is used to agitate the bed as in the biological satge dislodging the solid particulate matter that has
been trapped within the bed. This waste water is then discharged from this filter chamber.
It should be apparent that the biological stage never requires maintenance.
8. & 9.
These are simply the drain points installed on the filter chambers. They are located at the bottom of the filters and are typically plumbed with 50mm piping.
The bead filter. This is optional and provides a measure of water polishing – for the removal of ultra fine solid particles that may have made it past the
mechanical filter. As the load on the bead filter is likely to be low the pressure drop across the bead filter owing to clogging of the bead bed is likely to be
Return to Koi pond via a 55W unit (note that you should work on using 4W of UV per 1000 litres of pond water, despite manufacturers claims to the
contrary!). This has been detailed as simply as possible – in reality this return can be a waterfall or feature, or split into below surface returns within the pond
Waste line. This is the discharge line from the bead filter and it is often connected to the waste lines from the settlement chamber and the filters .
Waste lines are important to consider and often an opportunity is missed. Koi pond waste water is fantastic to use on gardens. It is rich in plant nutrient and
fantastic for grass. However, in the event that you are medicating your Koi pond you do not want to dump salty water or the like onto your grass. Bear this in
mind when plumbing your waste water line and give your self the option to divert water either over your garden, or to your sewer/street discharge.
Pump Fed Gravity Return Systems
Slotted feed pipe to pump.
Generally in our Koi ponds we use high efficiency low power consumption water pumps – the Pedrollo pumps we recommend are a case in point. Quite
often these pumps are not self priming and they do not have leaf traps built in as opposed to low efficiency high power consumption pumps which are
typically represented by swimming pool pumps. By using a slotted pipe in your settlement chamber you are effectively adding a free leaf trap to your pump
at very little effort or cost to yourself. Anything that makes it past the slot will be small enough not to trouble your pumps impellor.
The pump in this diagram is mounted above the water level of the settlement chamber. It would thus require a priming unit since generally these pumps are
not self priming units. You need to allow additional space to install the priming unit. If you are able to mount the pump below the water level of the
settlement chamber you will be able to avoid the use of a priming unit since the pump's impeller will remain flooded owing to the water level in the
settlement chamber being above the impeller.
By way of example the U/V unit has been installed directly after the pump before the primary mechanical filter, in this case a bead filter. There is no fixed
advantage or disadvantage to installing the UV light either before or after the filters on a Koi pond. Match your U/V to your pond size at 4W of U/V per
thousand litres of water. Also be sure to match the water flow rate from your pond to the size of your U/V. If you need more than one U/V it is always better
to split the water flow through each U/V in parallel and not in series. This minimizes the resistance to the U/V that your pump will face, and it increases the
contact time of the U/V lamp with the water flowing through it.
Note that you can never overdo U/V on a Koi pond. When in doubt opt for a bigger U/V lamp or double up with two smaller lamps.
In this example we have used a bead filter as the primary mechanical filter on the Koi pond. Equally this could be a mechanical stage filter similar to the one
shown in the Gravity Fed Pump Return model that we have already discussed. In this particular instance careful attention must be give to the bead filter to
ensure that it is backwashed more regularly owing to the fact that in its current position it will performing a higher level of duty than in the first example
where it was being used as a water polisher. Bead filters are excellent mechanical filters and the choice of location for a bead filter in your filtration systems
is one of preference and of practicality to suit your particular situation.
The biological filter – in this case our moving bed media biological filter. Remember to install the drain for this filter somewhere useful because although the
media is self cleaning and this filter does not require maintenance there may be times on the odd occasion when you may want to empty your filter.
The important bit.
Note that the exit from this filter is 110mm pipe that is then split into two equal 50mm or preferably 63mm pipes. It is important to ensure that you have the
ability to drain the biological filter faster than the pump can fill it or else you are going to be overflowing the biological filter. This is why the biological
filter is mounted higher than the water level of your Koi pond in order to get gravity to do the work of returning the water back to your pond. Even better
than 50 or 63mm diameter pipes to return the water to the pond, a 110mm pipe can be used! Quite often the biological filter can be hidden or constructed as
part of a waterfall/water feature of the pond itself which is one of the attractions of installing filter systems this way.
The issue is often brought up of circulation within the Koi pond itself. We have found that gravity return systems deliver as effective a circulation within the
pond itself as do their pump driven counterparts. Of course you can always make use of your skimmer circuit to help create and improve water circulation
within the Koi pond itself.
We also note that in our Koi ponds where air curtains / aerated bottom drains are used, the circulation within the pond is massively increased. We cannot
recommend the use of air curtains or direct aeration via air stones in a Koi pond strongly enough. Aeration within a Koi pond creates massive vertical
circulation of water within the Koi pond which boosts oxygenation of the Koi pond by an enormous factor owing to the increased contact with the surface of
the pond (which is where gaseous exchange takes place).
Air lift filter systems
Air lifts are extremely energy efficient in terms of moving large quantities of water through filtration systems. Deployed correctly a Koi pond can be run off
air pumps only – which when compared to the running cost of water pumps makes this an attractive option for the potential Koi keeper.
The drawbacks to airlifts are primarily those of design. They cannot be retrofitted to existing systems because they rely on very low heads – or water height
differences to function properly.
Airlift systems require large quantities of large diameter pipe – (at least 110mm) to allow for water to be drawn from the pond via bottom drains, and to be
returned to the pond. Because the relative flowrate through these pipes is slow, you need more of them. So in a normal pond where a single 110mm bottom
drain would be used, in the case of airlift systems you would need to make use of two.
Typically on airlift systems although you can get massive flow rates at low cost they cannot be used to drive something like a bubble bead filter or any
filtration that relies on pressure of any kind to function effectively. This does not mean that these systems cannot be used and it is of course possible to run a
skimmer off a conventional water pump that then feeds through a bubble bead filter before returning water to the Koi pond under pressure (ideal to use for
waterfalls or water features). You are still reducing your overall power and hence running costs on the Koi pond substantially by eliminating the larger
primary water circulation pumps that drive your filtration systems.
The drawing illustrated is an accurate model of the pond installed at our premises in Roosevelt Park. In other words, you can see it up and running anytime
you want to.
Slotted 50mm pipe. This line feeds the 55W UV (you need 4 W of UV per 1000 litres of pond water!) line which is powered by an airlift system (23.). The
UV by way of interest draws more power than the air pump pulling the water through it. The slots in the pipe prevent leaves and larger debris from blocking
the UV light. In order to change the globe on the UV which is done every 8 to 12 months, the stand pipes in the settlement chamber must be fitted and the
chamber drained in order to prevent the UV from flooding continuously. Alternately a 50mm valve can be installed in this feed line.
110mm slotted feed pipe to the filtration system. This pipe is a large diameter pipe and is used to feed the filtration system – the same system as we have
used in the other designs illustrated above.
Note that in the case of airlifts we use a two for one ratio by rule of thumb – each filter feed pipe of 110mm is fed by a settlement chamber fed by two
110mm bottom drain pipes. This maximizes the efficiency of the airlift system by minimizing the height differential between the settlement chamber and the
Note that when in doubt you can never overdo bottom drains in a Koi pond!
50mm piping from the UV light. 50mm on an airlift is sufficient to turn the water through the UV light a sufficient number of times per hour. In this case the
line is specified to the airlift feature (23.)
The airlift system at work in a feature. The idea behind this is to demonstrate how airlifts work and in this instance the system is configured to lift water from
one 110mm pipe to the next via a 50mm airlift pipe located in each. Via the 9 pipes installed water is lifted up a height of about 700mm above water level.
Naturally volumetric flow rate is sacrificed in order to achieve this height – and the flow rate of around 2000 l/hr would be increased to an estimated 10
000l/hr if the airlifts were all used at the same level.
An air stone. This is located at the bottom of the airlift pipe which in this case is a 63mm diameter pipe. As air passes from the air stone in the form of small
air bubbles they rise up this pipe with some velocity and as they do they drag water up with them. The pipe with the air bubbles located in it is installed
40mm above the level of the surface of the ponds water and as the water pulls up with the bubbles this overflows over the edge of the pipe, some 40mm
higher than the pond water, which is what causes it to flow back to the pond.
It really is that simple.
The drawbacks are as follows:
1. The level of the pond is important. If the pond level drops by a few cm the performance of the airlift system will be compromised. This is easily
overcome by installing a simple auto top up unit on your Koi pond.
There are a few additional notes:
The flow rates of the water up the pipe is what determines how much water the airlift system can move. The more air you push through the airstone
the more water will be displaced and moved up the pipe with increased velocity – thereby increasing the flowrate of water through the system.
The more air lifts you have the greater the flowrate of water.
The more 110mm pipes you have feeding the airlift system the less the water height difference at any point in the system - and the better the airlifts
The airlift pipes are approximately 800mm in length. The longer they are the more efficient – but this has to be seen against the depth against which
your air pump has to pump air (the deeper the less air the air pump is able to deliver).
By way of interest on this system we are running an 80W 80l/min air pump which is turning water over at a conservative 8 000l/hr through the system.
Included so that you can note the height of the air lift pipes. If you are in doubt make them longer than they need to be – you can always trim them to suit
when commissioning the filters.
110mm return pipe. In this case this pipe is returned directly to the pond through the pond wall (not illustrated). Of course you need to ensure that smaller
Koi do not try and swim up this diameter pipe but with a bit of thought this issue can be easily resolved by locating the return pipe in the Koi pond in such a
way that the Koi are not able to access it. Alternatively you can tee off and reduce to smaller diameter pipes, say 63mm (better) or 50mm (OK) which can
then return water to the Koi pond from multiple points.