All the detail you will need

Pond design

Keep it simple. Koi ponds should have nothing protruding from any of the surfaces into the Koi pond on which the Koi can scratch or injure themselves.

If you have to have a bridge over your Koi pond be prepared for the consequences. Koi will hide under the bridge continuously. They are difficult to catch under a bridge. If the bridge sticks into the water they can damage themselves on it.

Avoid stepping stones in the pond. These disrupt water flow and can present substantial dead spots where debris can build up.

Complex and unusual shapes can present problems. They can be solved but the trade off is increased expense incurred in solving these problems or on the high maintenance of the pond itself. If it is a statement or design feature consider keeping the pond as a water feature rather than a fish pond.

Koi ponds at entrance halls of houses is a common trend. These are always tricky - the pond is a feature rather than a hobbyists pond. Filtration has to be located somewhere preferably close by. Koi ponds tend to be interactive - a place where you can spend time with your Koi. As an entrance feature this is largely not possible however. Rather build a pretty water feature here and your Koi pond in your living space of your garden.

Turnover rates

Simple enough. Work out the volume of your pond. Say 4m x 6m x 1.5m deep (on average) gives you a volume of 36 000l. A turnover rate of once every two hours through a filtration system gives you a nett flowrate of 18 000l/hr.

This the volume of water your pump will need to deliver. Pumps are rated according to their maximum output, so we suggest you take your flowrate required and multiply this by 50%.

In our example this gives you a flowrate of 27 000l/hr. This is the size pump you will require.

In Koi ponds two is always better than one. So two pumps at 13 500l/hr is better than a single pump rated at 27 000l/hr.

If you cannot source a 13500l/hr pump, go for the next model up. This might be 15 000 l/hr for instance. In reality, depending on the pump you select you might realistically get anywhere between an actual 10 000l/hr to 12 000l/hr from the pump as it operates in your system.

It is just a starting point from which to build your Koi pond. It may well change later on.

Bottom Drains

In 36 000l of pond volume you will need three bottom drains since one drain per 15 000l of pond gives you 2.4 drains. Always round up. More drains are better than too few. Each drain is run independently - coupling them all up into one pipe line is not going to work.

Bottom drains should always be located at the deepest point of a Koi pond. Hence it is common practise to locate the drains equally spaced away from each other and the walls of the Koi pond and to slope the floor of the Koi pond down to the drain.

The bottoms drains sole purpose is to prevent the build up of sludge and detritus on the bottom of the Koi pond. Detritus and sludge go rotten in quick order and a breeding ground for bad bacteria which can wreak havoc on your Koi. It also ensures that your pond water will never be clear and you will not be able to see your Koi.

Settlement chambers

Think of settlement chambers as your first filtration stage. In this stage, solid matter in the form of detritus and sludge that are carried from the Koi pond's bottom drains are allowed to settle out in the chamber.

For this reason the settlement chamber must also have a drain located at its lowest point. Opening this drain will allow all the solid debris to be flushed to waste.

The settlement chamber is isolated from the main Koi pond by means of stand pipes. A stand pipe is simply an extension peice of 110mm pipe that is fitted on top of the pipes coming from the bottom drains on the pond, effectively raising the pipe from the bottom drain above the height of the pond, thereby cutting off the water flow from the pond.

This allows the settlement chamber to be drained of all water completely. In addition when the stand pipes are removed from the bottom drain pipes, water will surge from the bottom drain pipework which will flush these pipes of any debris that may have settled in the pipework. This water can be flushed to waste from the settlement chamber.

By doing this 'flushing' process you will rid your pond of a good 70% of solid debris manufactured by your pond and by your Koi. This effectively reduces the load on your mechanical filters by 70%.

Less load on your mechanical filters means easier maintenance for you.

Some Koi ponds operate without settlement chambers. These are not Happy Koi Koi Ponds. However, in some situations settlement chambers are simply not an option. If there is no way a settlement chamber can be incorporated you need to double up on your mechanical filtration to compensate.

Surface skimmers

A standard swimming pool weir can be used to great effect in a Koi pond. Locate surface skimmers logically, away from air curtains or airstones, and away from surface water returns.

Surface skimmers can run on their own pump, or they can be operated by pumps that are taking up water from the settlement chamber as well. The quantity of water being taken from each can be regulated by valves.

Often surface skimmers are used with their own dedicated pumps with the water returned directly to the pond for purposes of water movement (bypassing the filtration system entirely).

We do not recommend turning such pumps on and off. Water sitting in the piper work when the pump is turned off will become stagnant and the build up of bad bacteria will occur. When the pump turns on these bacteria are injected into the pond and can cause major problems for your Koi.

Mechanical filtration

Whether you have a settlement chamber or not, the mechanical filter's primary function is to ensure that no debris makes it past the filter before the water reaches the biological filtration stage.

This is because the biological filter operates at its optimum when there is no solid material in feed water. Even a small amount of debris entering the biological stage can severely compromise its performance over time.

Mechanical filtration systems require maintenance to flush out the solids entrapped within them to waste. This needs to be performed regularly before these solids start to rot.

Ultra Violet Lights

These are mandatory on a Koi pond. They serve the purpose of killing small uni-cellular algae plants that are responsible for causing green water (not algae growing on the sides of the walls of the pond). Once these algae cells are killed off, they clump together into larger lumps that can be taken out by your mechanical filter.

You cannot overdose U/V. At 4W per 1000l of pond water you also get a measure of sterilisation in your water - U/V at this intensity will kill fungi, some viruses and even some bacteria.

It does not matter where you install your U/V light. Only water in the U/V is sterilised so it cannot play a role on your bio filters, or anywhere else for that matter.

Far more important is to move water through the U/V slowly. Ideally you need to have the pond volume move through the U/V between once every 4 to 6 hours only. In other words, the longer water is exposed to the U/V the more effective it is.

U/V globes drop off in terms of how much U/V they emit. They only last between 8 and 12 months before they need replacement (despite them still glowing purple).

Biological filtration

Biological filtration is there to grow bacteria in colonies that are exposed to the water column in which the dissolved contaminants and waste products produced by the Koi and the pond can be reacted away.

Biological filtration generally requires very little maintenance. They should be maintained according to manufacturer's specifications, typically once a month or so.

Should more maintenance be required there may be a problem with the mechanical filtration or the pond may well be overstocked.

Plant/Vegetable Filters

Plant or vegetable filters are a great way of stripping out any residual wastes passing from the biofilter and would comprise a part of any Happy Koi koi Pond specification. Plants are planted in these filters which are simply shallow ponds that typically overflow back into the Koi pond. No soil is used.

It is a good idea to install a drain on a plant filter so as to be able to drain it to waste from time to time. Living plants produce mulm and mulch and detritus over time which needs to be removed.

Plants can also grow at a rapid rate in Koi ponds owing to the nutrient sources provided to them. From time to time excessive growth has to be removed and thrown away. Make it easy as possible to maintain your plant filter by means of access to it.

Water returns

Water can be returned back to the Koi pond anywhere. Use some logic in this process - you can return some water back via a waterfall for instance. The idea should be to return water as far away from the suction point for the filters as possible.

In addition you should aim at returning water back to the pond in such a way that this moving water should prevent any dead spots in the pond. Dead spots are areas where water lies stagnant without any water movement. These should be avoided entirely.

Water returns can be delivered at or just below the water line. They can also be delivered below surface level upto half the depth of the Koi pond. Depending on your pond you may want to return more water to one section of the pond than the other.

You can never have too many water returns. Put each one on it's own line and it's own valve so that you can regulate the flows and also so that you can shut the pond off from the filter system when needs be.

Piping, fittings and valves

Buy the best you can afford. These are a once off expense. A broken fitting or a fitting such as a valve that doesn't work properly will bring you misery for years.


One of the secrets to success in a Koi pond is oxygen. Maintaining maximum oxygen levels at all points in a Koi pond is not essential - it is a matter of life and death. In order to achieve this vertical circulation we make use of bubbles delivered by air curtains or air stones. As the bubbles rise up through the pond they bring water from the bottom of the pond to the surface where the gaseous exchange takes place. In turn the oxygen rich water of the surface is then pushed down to the bottom of the pond.

Vertical circulation ensures that at all points in the pond oxygen levels are kept the same and at their maximum values.

Venturis play a limited role in Koi ponds. Waterfalls should be seen as features rather than aeration devices (although they do aerate returning water well).

Maintenance and water changes

Regular maintenance of your filters will generally require water. Some pond water is removed in the maintenance procedures of your pond and a good rule is to change between 5% and 10% of the pond's water once a week in summer, and somewhat less in winter (typically 5% once every two weeks or so, depending on temperature and fish load).

Along with water changes it is important to replenish trace elements that are taken up by bacteria, algae and your Koi on an ongoing basis. One of the best ways of doing this is by adding montmorillonite clay when you are doing your maintenance. You cannot overdose with it with a typical dose being 20g per 1000l of pond water.

Filtration details can be found here