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Pond Construction

A Guide To Modern Pond Construction

Most of us will have started keeping cold water fish and then after seeing Koi at a Koi dealer or at a garden centre decided that this was the way to go regarding our fish keeping. Many of us will have started with a small, or not small, ornamental pond with very little depth and usually many plants including water lilies. These are very ornamental and look nice in the general setting of the garden, but totally unsuitable for the successful keeping of Koi.

Let us assume that you are now intending to build a pond and these notes are now intended to give some ideas and recommendations for your consideration before you make a decision.

There is a big advantage in belonging to a local Koi club because then you can visit other members' pond , exchange idea, often a club has books in the library which shows photographs of various ponds. There are now quite a few photos of ponds appearing on homepages on the Internet.

Let us now start looking at some of the things to consider before designing your pond. The position of the pond, the size and the shape will inevitably depend on one another so you cannot really decide on one without the other.

The first idea is to place the pond near to the house so that you can admire your fish even when it is cold and windy day.

You should keep the away from large trees as the roots especially in the case of species such as Weeping Willows will seek out of water and can damage the ponds especially in the case of pond liners. Bamboo has the same effect and will soon put down long roots and will easily penetrate the pond liner.


Safety is another consideration especially if you have young children. Your children may be grown up, but you are going to have grandchildren too. There is also the danger of children getting into the garden from next door. Children are very persistent when there is water around, and they cannot be watched all time. Another consideration is how close to the house you should build it. It must be remembered that with a six feet deep pond below ground then with the foundation and base with the initial hole will be eight feet deep and especially if there is heavy rain then there is a danger of the sides collapsing and even undermining the foundations of the house it self. If you are building the pond close to the house then it is important to get professional advice or swimming pool builders that  would put up temporary retaining structure when digging as deep as this. There is always a danger of a caving in especially digging out trenches. When working in this area make sure there is someone above ground, who can be at your assistance in case of accident.

Type & Shape

The first thing to decide if you want a formal or informal pond above or in ground.

Size of Pond

Everybody likes to make their pond as large as possible, but there are several things to take into account. The larger the pond the more maintenance and personal effortwill be required. To keep the pond in top condition for your fish.


Contractor – electrical – transport – consultation – aeration – pump – work – landscaping - after service feng shui design - filter media - waterfall (artificial or river rocks)

Bridge – pagoda – tables and chairs – pvc pipe and fitting.

Depth of pond

It is generally agreed by all books and experts on the subject that the pond should be six feet deep, and if you are building a large pond say 18ft x 12ft this is probably correct and looks right when completed. If , however you are building a much smaller pond then this depth does look completely out of proportion. In these case as it much better to have the pond say if the minimum depth 4 foot 6 inch with the depth of 5ft in way of a bottom drains.

Bottom drains

It is generally accepted that bottom drains are a must and should be fitted to all ponds under construction. These are a few cases where it is not possible to connect into the main drains but even in those cases the problem can probably by overcome by use of a soak away. If the main drain is above height of the pond then it is possible to have a discharge chamber, and then you can pump it to the drain, using a pump with a float level fitted.

The number of bottom drains required will depend on the size and shape of the pond and also the preference of the owner. With a rectangular pond say 12ft x 10ft then two bottom drains would be normally used, and with a pond by 18ft x 12ft then three bottom drains are usually used.

Filter System

We will now look at the filter system for the pond. This must be considered when you are designing your pond system, and you must decide on this important item before acommencing to construct the pond.

Many Koi keeper can quickly decide on what size of pond they want, but in many cases they do not have enough space to have a filter system big enough to support their designed pond.

When you have decided which type of pipe you are going to use then you need to decide if you are going the bottom drains directly to the main drainage or to the settlement chamber of the filter system. The sketch below show the different ways of doing this.

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The diagram above shows a typical pond layout where the bottom drains go direct to waste, and the feed filters are taken from mid water.

The stand pipes in the discharge chamber can be lifted to release the water to the main drain. Slide valves used instead of the stand pipes.

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The diagram above shows another pond layout where the bottom drains constantly feed the first bay of the system, which in fact is the settling chamber. The drain from the settling chamber is connected to a slide stand pipe, in the discharge chamber.

This method continuously removes waste from the pond, but it is necessary to have a very efficient settlement which is cleared regularly.

The surface area of the filter system should be one third to one half of the surface area of your pond. This will important as when your fish grow, and the pond is heavily stocked with fish then the filter will still be able to provide good water quality and so ensure your fish can be maintained in good condition. It is important to know the exact gallonage of your system.  The exact volume is important to ensure that dosage of medication can be applied accurately at a later stage. It is also a good idea to know the capacity of your pond and your filter system separately.

Filtration method

Mechanical – biological – chemical – vegetable – sand pressure filter – trickle tower

Settlement chamber feed by bottom drain – or forced removal dirt with air pump and uniring timer (to remove the waste at regular intervals timer operates at one minute at preset intervals) or using vortex chamber for removing dirt.

Mechanical filtration is the only really filtration. All the others change the nature of chemicals they come into contact with.

Biological processes to purify the water – bio filter supports a colony of aerobic bacteria that convert toxic ammonia to nitrites then to nitrates which is absorbed by growing plant as fertilizer and plant protein becomes food for the fish thus complete the cycle.

Chemicals which extract organic wastes, inorganic chemicals & carbon dioxide from the water  

zeolite – activated carbon

zeolite 1kg + 50 gal water

carbon 1kg + 50 gal water

Flow rate

Must be in tune with filtration processes at work. Too powerful circulation will prevent the build up of beneficial colony of bacteria by tending to dislodge them.

Mechanical removals of solids detritus as the water passes through a suitable medium such as "Clarenet" – "Bristle Brushes" – "Synthetic Fiber" or Vortex.

The second purpose of a "Proper" Koi pond filtration system is that of a biological filtration Koi produce toxic substances that become totally dissolved in the pond water and cannot be strained out by mechanical means.

It is important here to understand that a good biological stage is not intended to be a "strainer as in mechanical stage".

Filter Media

Baked clay granules – ammo rocks – gravel – coral – sand – foam – brushes – flocor – bio home – plastic moulding – synthetic fibers cartridges brushes springflo – siporax etc.

The next stage is a chemical or vegetable filtration.

Final to polish the water use of sand filter and trickle tower.

An overflow is usually incorporated in one of the bays so that the pond water cannot go above a designed level.

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Figure shows the general layout of a simple 3 bay filter system, and this is what you should aim for. On the right hand side water enters the filter system from either the vortex chamber, mid water suction, or drains.

The water then goes to the bottom of the first chamber and then raises up through the media grids and the top of the chamber. This water will then overflow over the weir, and so to the bottom of the second chamber process continues as it did in the first bay. When it reaches the last bay it is pumped back to the pond.

There has been quite a lot written about these chambers, and I have seen several comments which said they cannot work because centrifugal force requires very high revolutions. This is true if you are comparing it with a real centrifuge, but even at the speed at which the water goes around the chamber it is sufficient for the heavier solids to drop to the bottom and remain there until they are drained away. The amount removed in this way proves that it is working Smaller floating debris like algae will not be removed, and will still be carried over into the first filter chamber.

The efficiency of the unit does depend a lot on it’s design especially the diameter, height, and especially the positioning of the inlet and outlet pipes. The pumping rate can also be very important.

If you have any doubts about the efficiency of a vortex chamber then do try to visit a pond keeper that has one in use as I am sure you will be quite impressed with it.

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This rough sketch shows the basic idea for the Vortex chamber. The inlet from the bottom drain passes through the inlet just above the cone section of the chamber. The inlet is positioned so that the water flows around the side of the vortex, and then rises up and out through the outlet at the top, and then passes into the first chamber of the filter.

The solids will then fall to the bottom of the cone, and can then be flushed out to the main drain several times a day with the minimum loss of pond water.

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When someone is starting to dig out their pond they often ask what size to allow for the vortex chamber considerably in size. Even when you have decided to have a 36 ins or 48 ins diameter unit the heights do manufacturer to the other. They can be from 36 ins high up to 84 ins. For this reason it is essential to pump before you start digging so that then you can dig out the area where the chamber is to be fitted to the cone.

Quite a few of these vortex chambers are free standing, but some of them have to be buried in the soil. They should be stood on a six inch thick concrete base.

In the case of connection to a Vortex then it will be necessary to use more than one elbow to connect up is still necessary to make the flow as smooth as possible.

Circulation Example

System up to 5.5 tons (1,200 gallons), Flow rate approx 550gph

System up to 12  tons (2,600 gallons), Flow rate approx 950 - 1,150

System up to 30  tons (6,600 gallons), Flow rate approx 1,800 - 2,000gph


Output - watts - cost
Air pump - 60lph - 80lph - 100& 120lph

What to include in the walls

Whilst we are building the walls we must remember that there are some pipes and items which must be included in this stage. Consideration of the following should not be neglected :-

  1. Power skimmer

  2. Return from power skimmer

  3. Return from main pump

  4. Deep water return

  5. Mid water section

  6. Water fall

  7. Venture

  8. Spray bar

Power skimmer is an important item for removal of any leaves and surface debris, and they make a remarkable difference to the clarity of the surface water. They are fitted with a basket, which can be removed for removing the leaves, etc. when the pump is shut off.

Applying proper system maintenance

Pull bottom drain regularly (if no uniring)
Partial water change (10% daily change)
Keep pond & filter as clean as possible
No overstocking
No over feeding
Quarantining new fishes
Observing pond & Koi closely
Regular water test (Ammonia, Nitrite, Nitrate, pH, do and Hardness)

Don't try to keep Koi, learn how to keep water, then the Koi will "keep themselves"

The above was prepared by Mr. Hans Ham of ZNA Malaysia Koi Club. If you wish to seek his further opinion on Pond Construction, please post your message at the KOI Discussion Board. Comment are welcome.


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