Build your own Koi pond filter system

There are a few rules of thumb we follow...

These are not hard and fast rules - they are more guidelines we use when designing Koi pond filter systems. It's easy really, once you know how! The knack is knowing how of course!

1. Your Koi pond size will largely determine the size of the filtration system you will need. The larger the Koi pond the larger the filter system!
2. Koi pond size will determine turnover rates - the rate at which water should flow through your filter systems. Typically I use the following:
   Ponds between 10 and 30kl - once an hour
   Ponds between 30 and 60 kl - once every one and a half hours
   Ponds over 60kl - once every two hours
3. You will need a settlement chamber - see how to build one here - and aim at between 3 and 5% of total pond volume for this chamber.
4. After the settlement chamber you will need primary mechanical filtration. This is then followed by primary biological filtration and then a final polishing stage if required.

I prefer gravity fed filter systems. In other words the pump is located at the end of the filters and returns the water back to the pond. It means that the filter system will be fed with water via gravity (hence the term 'gravity fed').

Let's start with a few pictures...

Section of Koi Filter System

Plan View of Koi Filter System

You don't have to build these chambers as one long run. You can build them in a square, or a circle or in any form the suits you. See the pics below...

For every 15 000 liters of water that you aim at pumping through the system you will need one 110 mm pipe connecting the chambers to each other. If you use less, the water level in the chambers will drop by too much and your system will not work as it should.

For every 10 000 litres of pond space (in which you will keep 10 fish max!) you will need to run approximately 100 litres of Active bed media. This means that the primary biological chamber needs to be at least 300 litres in capacity per 10 000 litres of pond volume. This allows you enough upgrade ability later on if you want to double up on your Active bed media you can do so.

On chambers using active bed bio media you will need to ensure some mechanism to ensure that the active bed bio media doesn't escape the chamber. We use 110 mm pipes with an end cap on the end and slots cut into it using a thin blade on an angle grinder. Crude, but effective!

Note that if you are completely mad and bonkers and NOT using active bed bio media you may well need a very much bigger chamber to get the same filtration capacity. Check with the manufacturer of your media and make sure you give yourself enough upgrade room for future expansion...

In your final chamber, which we normally leave as a blank you can add oyster shells, or use it as a final polishing stage with Japanese matting, or brushes, or whatever you like. But if you follow this design reasonably accurately you won't need anything in there. The water in the final stage should be crystal clear and ready for your pump to suck the water through it and return it via your UV to the pond.

This design gives you maximum pump efficiency. This saves you electricity money over the long run.

Note that the white pipe is the stand pipe for the settlement chamber. So bottom right is the settelement chamber flowing to bottom left which is where mechanical filtration takes place. Then the third chamber which is a active bed bio media chamber - top left - feeds the last chamber (top right) which is where the pump sucks clean water to return to the pond.

This is the settlement chamber. Note the drain at the bottom! The pipe in the left hand wall is a 110 mm pipe that simply projects into the next chamber.

This is the final chamber - the pipe at the bottom is the suction line from the pump. What isn't clear is that this chamber too has a drain (for just in case). This chamber is fed by the 110mm pipe sticking out of the left hand wall.

And of course the pond. About 12 to 14 000 litres in all...