How to build an Eco friendly modern Koi pond

As with any pond construction project, careful though was given to the siting of the new ponds and fish house, and in this case one of the most important aspects was to locate the fish house where it would gain most heat by choosing a position in full sun for as much of the day as possible, both Summer and Winter. Our premises are surrounded on three sides by very large and mature trees, which means that much of the ground is at least partially shaded even in Summer, so we decided to locate the new ponds at the north East perimeter of our site, as far away from large trees as possible. This however meant running services, water and electricity 50 yds from our existing fish house to the new unit, and therefore incurring some extra expense to lay on these services, but in our view well worth the investment.

The design objective were :-

• To construct two ponds, inside a commercially available 'off the shelf' greenhouse to provide the necessary protection from the elements and to provide protection from the weather and better heat gain.
•  The construction design called for a fully insulated structure, so that both walls and floor of the ponds would be effectively insulated to reduce heat loss.
•  To provide modern and efficient filtration which would be easy to maintain yet would provide excellent water quality even at high stocking levels.
•  To minimise running costs by use of substantial insulation materials and energy efficient electrical equipment.
•  The use of ultra low wattage pumps and electronic UVs was therefore an absolute must.
•  To provide truly energy efficient heating, which along with the construction methods, position, and greenhouse enclosure would provided the most energy efficient package possible.  To achieve this goal, we had decided to install a DC inverter air source heat pump.
•  The fish house was to be 20ft x 12ft containing 2 ponds, one of approx 3000 gallons and one of approx 4000 gallons.

The site chosen for the new fish house had already been used previously as the site of one of our large semi natural growing on ponds which is no longer regularly used. So this was emptied and the liner removed. This had been around 2ft deep on average. First we carefully drove a hired 3 ton digger down into the old excavated area and dug out the area to be occupied by the new ponds to a depth of around 6 ft below the original ground level. This took less than one full day. In this case we drove the digger ourselves - its really great fun! However it is worth the extra £120 or so to hire an experienced driver as getting the hole square, with a level floor and clean cut vertical walls (as far as possible) can save a fortune on hardcore and other backfill materials.

The spoil removed was heaped up alongside the excavation as this would later be used for backfill and making good soil levels.
The picture (right) shows the excavated and prepared area, with the floor levelled and a rough area dug out where the filters would ultimately be located. The picture shows the bottom drains, just laid in the approximate position that they would occupy.
To aid with the levelling of the site, a tripod mounted laser level was used, these can be hired, but now simple models can be purchased for as little as £60 and these make the job of levelling any site very easy indeed.

The next stage was to measure out and mark with pegs the wall positions for the ponds, so that the correct positions for the bottom drains could be established. The drains were then set on circular pads of concrete, checking that they were oriented correctly (with the outlets pointing squarely toward the filter area) and absolutely level.

The concrete was left to cure for 24 hours before any further work was undertaken. Here we use circular plastic templates (cut from an old water butt) to make the formers for the concrete pads. The concrete was benched up around the drains to ensure that they would be held securely in position whilst the bottom drain pipe work and concrete floor were laid.

Next we barrowed in soft sand into the excavation, which would act as a flat, level and well compacted base on which the floor insulation material was to be laid. This is the correct and recommended type of material to use as a firm and level base for the insulation which was was 50mm Cellotex board. The sand was laid to a depth of 50mm and was levelled and well compacted down using a plate compactor before the board was laid.

The sand base was completed and Cellotex insulation applied across the whole floor area of the pond. Then the bottom drain 4" pipes were cut to length and glued into position in the bottom drains. Swept 4" bends were used to convert the horizontal pipe runs into the vertical pipes that would connect into the filter chamber, taking great care to ensure the pipes entering the filter chamber were vertical and then both bottom drain pipes were supported in position with more concrete round the swept bends to hold the pipe runs securely in place.

The picture (above) shows the completed base ready for the floor slab to be laid.The picture (left) shows a close up of the bottom drain and pipe work installation and support.

The next step was to lay the reinforced concrete floor. This was formed using 8" (200mm) thick Gen 3 grade concrete reinforced with plastic fibres which was delivered to site premixed. Ready mix is a much better , faster way of laying a concrete floor or raft foundation and ensures that the whole floor is of a consistent mix, and is laid in one go for maximum strength and integrity. Our floor used 5 cu metres of concrete, not a job to undertake using a small on site mixer! The plastic fibre reinforcement represents a much better method of reinforcement than steel in our view as the reinforcing material is completely inert and is not affected by ground water or chemical attack.

It is also easier to work with than conventional rebar mesh, which cannot properly reinforce the area around the bottom drain and pipe runs unless much greater depths of concrete are used.

Also, rebar mesh is invariably rusty when installed, and unless specialist methods are employed, will continue to rust in situ over the years and can eventually crack the concrete base - not normally a problem in a mass concrete building foundation, but not particularly desirable with the floor of a pond!

Once the floor had been allowed to cure for around 3 hours, we trowelled up the base to a smooth finish using a steel float.

The picture right shows the completed base, along with the first stack of 140mm hollow concrete blocks which have already been positioned ready for laying.

Now we are ready to start the wall construction. Here we opted for 7 Newton dense , hollow concrete blocks 140mm. Hollow blocks are considerably lighter to lay than solid blocks and key together very well when laid, as excess mortar automatically expands into the voids.

They can also of course be backfilled with aggregate (pea shingle) or a weak concrete mix to further improve strength and integrity. Blocks should be laid conventionally on edge, and do not need to be laid flat on their sides - this really does little to improve strength (better to use a bigger block in the first place) but can double the cost of the block work required - not a really sensible idea.

 First we set out the building lines, marking out the corner and wall positions on the base, and then checking the squareness of the construction by measuring the diagonal dimensions, corner to corner to ensure the walls would be parallel to each other and that the whole construction would be square. Then we started by building the corners first as illustrated (left)

All the corners were built first, this is the most difficult and time consuming part of the construction, as obviously we must continually check that the walls are vertical and square and each course is level.

 One of the biggest problems can be to ensure that each corner being built, is the same height, exactly , course for course, as each other corner. As the distance between corners here is up to 20 ft, we clearly could not use a conventional level, so we used a tripod mounted laser level to mark the intended height of each course on a wooden stake hammered into the ground just outside each corner of the concrete base.

 Basic laser levels can now be bought for around £80, or really professional ones hired as required. Once the corners had been constructed, the walls could then be filled in, a much faster and easier part of the build. (see right)

Here you see the wall construction nearly completed, with just the centre dividing wall between the two ponds to be finished. The dividing wall was built using exactly the same sized blocks as the rest of the construction. (see left)

Right, note that holes for return pipe work were pre-cut before the blocks were laid. This is much easier than trying to core out holes for the pipe work after the construction is completed.

The picture above shows one pond completed - and two of the three pond returns can clearly be seen in place - one near the top of the wall at the top left, and one tangential return, five courses down near the centre of the picture.

The picture - right shows a 3" main drain pipe laid into the excavation, at one end of the build and at low level. This would be used as a drain to waste for all water from the filters.  It also shows the Cellotex insulation board in place against the built wall.

In addition one of the 1/5" return pipes can clearly be seen in place - this one feeds a deep water tangential return, 5 courses down, which would be used to improve water circulation, and also act as a return for water purified via an ozone system.

Once the shell had been completed and the Cellotex insulation put in place against each wall, the entire excavation surrounding the main shell was backfilled with a weak concrete mix to a depth of 18" to give support to the lower wall areas and add strength to the structure. On top of the concrete the excavation was filled pretty much entirely with pea shingle. This was used to embed return pipe work at mid water level, as it does not compact and allows pipe work to move. Pipe work near the surface was bedded in soft sand.

Next all the pond return pipe work was installed, using pvc pressure pipe and swept bends wherever possible to induce better water flow and reduce frictional losses in the pipe work. Note the large bore (82mm) black waste pipe used for all water drainage to waste.

With the shell of the ponds completed (right), we completed the installation of pond return pipe work, and bedded all high level pipe work in sand to allow for movement and to reduce any risk of compaction.

 Then the peripheral areas were finished off with top soil to complete the backfilling exercise. We then added one more course of 100mm block work to the top of the outer shell walls, which would later form the base on which to mount the greenhouse. Note the Cellotex insulation right up to the top of the wall areas.

Next we constructed the filter chamber area. See left. This was built from 100mm dense concrete blocks, on a strip concrete foundation placed at a depth which would allow for the depth of filter systems which we were planning to use.

For easy access, a set of steps was built into one side of the filter chamber. (see left). The whole filter area will later be covered with a purpose made insulated building.

Next we rendered all the internal walls of the ponds with a special mix to waterproof and reinforce the entire structure. It is this render, which when properly mixed and applied massively increases the strength of the structure. The render is a mix of 2 parts soft (building) sand to 1 part cement with reinforcing plastic fibres added.

 One coat only is used to a depth of 5 - 10mm and this should be finished with a steel float to provide the necessary smooth finish. Multiple coats are not necessary or recommended since 2nd or subsequent coats using the plastic fibre additive will not bond as well.

 It is very important to use this strength of mix with the fibres added to give the necessary degree of strength and waterproofing. Weaker mixes, using multiple coats and without the plastic fibres will quickly degrade and eventually fail since the structure is essentially always wet.

 We are not plastering an internal house wall here but an in ground structure which must remain waterproof and withstand the adverse conditions. When applying to the floor area, a mix of soft and sharp (plastering) sand can be used to make the application quicker and easier and the depth of render can also be increased, but the strength of mix with the addition of plastic fibres is still vital.

To finish the shell of the complete structure, including the filter area, we then rendered both the inside and external surfaces of the extra block course forming the green house base, and added extra insulation inside the filter chamber to the dividing wall, and then concreted the filter floor. (Left).

Once the pond had been rendered, we then added fillets all round the base and walls of the ponds, using the same render mix as for the walls. This essentially will aid water flow and add strength to the junction of walls and floor as well as giving a better seal between the floor and walls. (Left).

Once the rendered finish was fully dry and cured (after around 1 week), we went over the walls using a hot air gun to burn off any plastic fibres that were standing proud and then painted the ponds using Gold lable epoxy pond paint. This is a three coat system which is easily applied with a normal paint roller, is reasonably quick drying and gives a deep gloss finish once cured. In the picture above you can see a pond after the application of the first coat, and during application of the second coat. After the second coat was dry, the walls were lightly rubbed down with worn out abrasive paper, just to remove any remaining plastic fibres which were still exposed.

We also finished off the shell structure by laying two courses of engineering bricks round the external walls to bring the greenhouse height to the desired level. Then we started with the construction of the greenhouse itself (see left). The sides and ends of the green house are built first as complete units, then bolted together in situ and then the base brick course was drilled in several places so that the greenhouse frame could be bolted down.

Greenhouse frame finished - note the staging inside the greenhouse - required to stand ladders necessary to reach the apex of the roof.

Here we see the pond walkways being built inside the greenhouse. To maximise pond sizes , we opted to build walkways over the ponds, rather than round them, so that the whole area inside the greenhouse is water - Japanese style! These walkways would be completely encapsulated underneath and to the sides with pond liner material, so the wood work will not get damp and rot. They were then decked.

Greenhouse fully glazed with 4mm Polycarbonate - obviously much safer than glass but also giving a much greater degree of insulation and heat retention. Thicker polycarbonate can of course be used if required.

It wasn't just the ponds we wanted undercover - here (left) we are building a complete filter housing over the filter area which would be, like the green house - finished and covered with polycarbonate for heat retention and protection from the weather.

Above:- Ponds all finished and filled with water and with the decked walkways completed and ready for Koi !

Above:- New Koi house completed with filter housing now also completed

Now we were ready to begin the installation of the filter systems. Here we had chosen Nexus filters for each pond, each coupled to a Cetus prefilter sieve. Of course the choice of filtration for your pond is a very personal thing, and people have strong views about various types of filter, but we have been using and fitting Nexus filters to customers ponds for around 5 years now, and we know they work very well when installed correctly and in the correct environment. They are extremely easy to maintain, give excellent water quality and are very compact. Also, they can be used with low pressure, low wattage pumps to reduce running costs, and in this installation, reduced running costs were a must. They are also the only filter on the market where more media can be added to cope with a higher fish loading as the stock increase or simply grows. Of course they can exhibit some annoying little faults, but later in this article we will explain how to get the very best out of them with minimal work and some simple modifications. However to ensure the very best from any filter , regardless of type or make, its pretty much essential to use a pre-filter in the shape of a large Vortex, or better still a sieve to remove as much of the solid detritus before water enters the filter proper.

Initially when sieves were first launched it was thought that they could only be used with pumped filter systems, but we came up with a simple and effective way to use them on all gravity filter systems as well, and we are happy to say that our design has now become the industry standard for all sieve installations. The pipe work layout when using a sieve is a little more complex than normal, but the following pictures and accompanying text should serve to explain all. The first thing with any filter installation is to make sure you plan the size and depth of the filter chamber round your preferred filter system, allowing plenty of room for plumbing, pipe work and all necessary electrical gear. Allow enough depth to install the filter components on blocks, so there is no pipe work, valves etc actually touching the floor. Most filters need a 4" inlet connection from the bottom drain, and if 4" bends are required, they take up a lot of space and depth, so ensure you allow for this by making the filter floor 6" or so lower than you really need.

Above - Smaller 3000 gallon pond using Nexus 200 and Cetus pre-filter sieve, with basic bottom drain pipe work in place, connecting both filter and sieve.

Above - general filter chamber layout during installation

Above - Larger 4000 gallon pond using Nexus 300 and Cetus pre-filter sieve, with basic bottom drain pipe work in place, connecting both filter and sieve. Note drain hole in the floor of the filter chamber to help avoid any possibility of flooding

In our filter system design, we had the Cetus sieves mounted on 3 x 100mm blocks laid flat and bedded in mortar. This provided for the water level in the ponds, when full to be 50mm below the top of the Cetus - just as the manufacturer recommends. The one design fault with the Cetus is that the main 4" lug to which you must connect to the bottom drain pipe work using a rubber 90 deg bend is way too shallow, and without support for this important joint, the connection can actually come off over time. To overcome this, we use a 4" rubber socket, instead of the rubber 90 deg swept bend supplied, to join the Cetus to the main 4" pipe which comes up right under the connecting lug, and this in turn is supported from beneath by block work, so there is absolutely no way the 4" joint can come adrift. (see below)

Then the 4" pipe work was supported as well, at various points, to ensure no strain on the pipe work when full of water. Using any sieve, water from the bottom drain feeds both the sieve and filter in parallel, not in series, so that the filter system will still work normally whether the sieve is running or not. When the sieve is running water is drawn through the bottom drain pipe, into the sieve and then the cleaned water is pumped back into the same bottom drain pipe, just before it enters the main filter using a separate pump. Providing that the pump powering the sieve is the same power as, or more powerful than the main filter pump all the water coming through the bottom drain pipe will pass through the sieve first, and therefore all the water entering the filter will be pre-cleaned.

Above - Close up of the correct way to connect the 4" inlet pipe to a Cetus - the 4" pipe joint you can see is firmly supported on blocks to prevent movement, and a rubber socket joins pipe to Cetus.

Left - Complete Cetus circuit showing 4" feed to Nexus, "T" joint joining the 4" pipe into back of Cetus - then a 2" return from Cetus re-enters the 4" pipe in the right hand side of the "T" joint you can see under the 4" slide valve at the Nexus inlet. Note the 2" purge pipe to waste controlled by the 2" ball valve (orange handle) which you can see in the centre of the picture - this allows the correct purging of the bottom drain pipe to keep it clean at all times. The Cetus waste 2" drain pipe is in the foreground at the bottom of the picture. Note also the extra take off point added to the base of the Cetus controlled by the black slide valve - this will be used to connect another pump which will drive the ozone system reaction pipe work via a venturi.

Above - Close up of one of the Cetus pumps - here we used Optimax 10,000 and 15,000 for their ultra low wattage. Note the swept bends.

Both ponds use Yamitsu 55 watt electronic UVs and Secoh 80 lpm air pumps. Yamitsu, made by Kockney Koi, are not only really good value for money, but are one of the only UVs on the market which are fully CE compliant, use standard Philips long life bulb technology (really the ONLY bulbs which are worth having) and use electronic controllers, so that the power consumption of a 55 watt rated UV is actually around 40 watts! Conventional ballast resisted UVs with mechanical controllers can use as much as 150 watt per 55 watt UV - quite a difference. Secoh, in our view, make one of the best air pumps ranges on the market, from 20 lpm to more than 200 lpm, and are very reliable, quiet and are fully serviceable, with the full range of spare parts being available from UK distributors.

All return pipe plumbing used 1.5" and 2" pvc pressure pipe, and as many swept bends as possible to reduce friction losses in pipe work. Return pipe work is fully valved using ball valves to separate every component, pump, UV and filter so that everything can be removed for servicing if required without the risk of flooding. UVs and pumps are all fitted using single union threaded de-mountable connectors to make removal easy if required.

In our systems We used a Red Devil 150 DC induction pump for the main Nexus 300 filter pump with an Oase Optimax 15,000 powering the Cetus for our larger 4,000 gallon pond. On the smaller pond we used an Oase Aquamax dry 8000 on the Nexus 200, and an Oase Optimax 10,000 on the Cetus. Optimax pumps are ultra low wattage, the 10,000 model using only 65 watts and the 15,000 model only 85 watts - again all aimed at reducing electricity consumption. Optimax pumps are classed as water movers and have poor head characteristics, so are no good for water features such as waterfalls or fountains, but are absolutely ideal as filter pumps, especially on applications such as sieve pumps, as pipe runs are invariably short, and 2" pipe can be used throughout, so flow losses can be minimised.

The decision to use one of the Blue Eco (was Red Devil) pumps was an experiment - we had heard very good things about them, so had to try one - and I have to say we are very pleased with its performance. These pumps use DC induction motors (direct current) which makes them way more efficient than AC motors - in a conventional AC motor, much of the electrical energy is lost in the form of heat, this does not happen with DC motors, and the energy consumed is much more efficiently used to turn the impellors, not heat fresh air. DC motor technology is rated at around 94% efficient, compared with around 45% for a conventional AC motor. In addition, DC motors are completely controllable, and by adjusting the power applied, we can reduce or increase the revolutions - anywhere from 30 - 3000 rpm to increase or reduce the water flow.

This is actually very important, as we cant practically work out frictional flow losses in pipe work and plumbing, and therefore normally the decision of which pump to use, in terms of power and flow requirements is little more than guessology, as its not until the pump is installed and the system run that we can actually measures the flows. In addition, flow rates can now be simply increased in Summer when we may need a higher turnover rate, to match the higher organic load on the pond, and can be reduced in Winter, when we only need a much lower turnover rate. The flexibility and controllability of these pumps also mean they can be used for a very wide range of applications from normal filter applications, water features such as waterfalls and fountains, bead filters which need much more power, and Trickle towers which similarly need high flow rates.

Here we are using the Blue Eco 240, the smallest pump in the range, but still capable of producing flows up to 4800 gallons per hour at 3000 rpm. We have set ours to 1750 rpm, at which speed it produces around 2000 gallons per hour and is using - wait for it - just 77 watts !

Above - Showing simple return pipe work arrangement from Blue Eco pump, through UV and then splitting the return via a "T" joint to the two top level returns in the pond. The open ended return and ball valve (top centre right of picture) will be used for the ozone injector system which will return water via the deep water tangential return seen earlier.

Above  - Blue Eco pump showing 2" inlet and outlet connections .

Above - Blue Eco controller - allowing full control between 50 and 3000 revolutions - which equates to 0 - 4850 gallons per hour.

Left - Smaller pond showing return splitter after UV into two - note the short return (top left ) is valved to force water through the longer return pipe, immediately underneath it. Please also note the ball valve immediately after the UV to stop all water flow in the event that the UV needs to be removed for attention. The open ended pipe terminating in a ball valve lower left in picture will be used for the ozone system return to the deep water tangential return.

Above - shows pipe work arrangement from Nexus outlet through pump, and also clearly shows the overflow system installed in the Nexus outlet chamber which joins onto the Nexus waste outlet manifold at the base of the filter

Above - shows pipe work arrangement from Nexus outlet through ball valve to pump, and also shows the overflow system installed in the Nexus 300 outlet chamber which joins onto the Nexus waste outlet manifold at the base of the filter. The return pipe at top left of the picture will be used for the ozone disinfection system

Above - Shows the groove designed to house a plastic weir plate (not shown) which is designed to be used during backwashing to prevent water flowing in or out of the Nexus. Unfortunately this really does not seal properly as it is very loose and ill fitting

Above - The easy (and correct) solution is to use a 4" slide valve at the base of the Nexus inlet pipe as shown in the lower picture and throw the plastic weir plate in the bin!

Above - shows the standpipe used when backwashing Nexus - this sits in the central tube as shown in the picture lower right. In its standard form the soft ribbed rubber collar pushes into the base of the central tube of the Nexus, sealing it off during backwashing, but because the ribbed rubber is only secured to the pvc tube using cable ties, the rubber sleeve slips up the pipe and will not seal the tube. This is easily remedied by bonding the rubber boot to the pvc tube using gold lable sealer.

Above - The standard s/s weir plate on the outlet chamber shown topped off with a tailor made piece of Jap matting to stop any Kaldnes getting into the exit chamber. The standard plate is too low and Kaldnes can easily escape.

Above - Eazy mechanical filter chamber shown with standpipe in place for backwashing. In its standard form, when backwashing, Kaldnes will bubble over the top of the tube and into the central pipe where it is definitely not wanted.

Above and right - completed filter installations - above on smaller 3000 gallon pond, and right on larger 4000 gallon pond. Note that most of the floor area has now been decked - this is used to cover much of the pipe work, and means that we are not having to avoid pipes when moving around the filter chamber. It also makes the whole area much neater.

One of the last jobs was to install an air source heat pump on the larger, 4000 gallon pond.

 The heat pumps we have chosen are 2nd generation DC inverter heat pumps - so ultra efficient. The model installed here is a 6kw output (20,500 btu) unit which is rated at around 1 - 1.5kw input max, so in theory this unit should be 5 to 6 times more efficient than a conventional electric heater, and at least twice as efficient as the most efficient condensing oil or gas boiler.

 Installation was simple - as we hope you can see from the picture - Water from the main filter pump flows through the unit (which has its own titanium heat exchanger already built in) and then returns to the pond - then just plug in to a standard mains socket - no heavy duty cables required - so its just as simple as fitting an ordinary in line electric heater.

 The installation positioning is important however as the unit sucks ambient air through one side (the rear of the unit pictured) and blows out cold air from the fan you see at the front. Heat pumps should be installed at least 30cm from the ground, or floor, as remember cold air sinks, so on a cold day air near the ground will be considerably colder than air even a couple of ft higher.

 With this installation, siting the unit inside the covered filter bay allows it to draw in slightly warmer air, but also means that its operation actually cools down the filter chamber considerably.

 See our page on heating for more detailed information on our range of air source heat pumps.

We are now testing the units performance over the next couple of months and will monitor and report our findings on a regular basis - but early results are pretty spectacular with the unit performing as anticipated but using way less electricity than anticipated. So great stuff so far.