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Which filter for my koi pond ?

Which filter for my koi pond ? 

Before becoming a koi lover, you have to become a water manager.

A very wise expression.

Which nobody wants to hear.

Most people prefer to jump directly to the adventure of having many colourful jewelry swimming in the water.

Many times it goes well.

For a long time.

But there will be always THE moment. 

The moment of green water.

The moment of koi with injuries.

Perhaps even the moment of dead koi.

And then you will loose the joy of having koi.

You would not be the first to acquire this position.

I know we repeat ourselves. We – from Koi Hacienda – do not get tired in insisting, that to enjoy koi, you need to plan from the beginning the project.

Patches and odd jobs – generally – do not last long.

The filtration system – a part of the construction of the pond – is the heart of koi project.

Which filter for my koi pond is an essential question that every koi lover should ask BEFORE starting the project.

Which filtration system depends on several factors:

  • available place
  • pond volume and koi population
  • your own budget

Good News: It is impossible to have a too big filter  

a) available place

Generally gravity filters tend to occupy more room than the pressure filters. Depending on the type of gravity filter, you will have to take into consideration an excavation next to the pond.


b) pond volume and koi population 

Here we are in the same situation as with the chicken and the egg – what first? Do you decide first the dimensions of the pond and then adapt the amount of koi? Or do I know that I want to have 12 koi?

There are exact formulas to calculate number of koi, feces, the square metres of biological material of the filters, but I will not go so far today and talk only about general rules.

Traditionally 1,000 litres are calculated so that a koi can develop perfectly (perfectly in this sense means a good body shape and a size of 1 meter). So you could also say 1,000 liters for 1 meter koi – the equivalent for example for 5 koi of 20 cm. But of course … we must bear in mind that koi – under optimal conditions – often grow quite large. In two years, those 5 to 20 cm could have reached 40 cm. Then what ? Respecting the rule, you should remove at least 2 …

Nor it is plan to put 1 koi of 10 cm in a pond of 1,000 litres because in about 7 years it might have grown to  1 meter.

With this information I only would like to put you on enquire for the topic “pond volume / quantity of koi.”



Attention: In the packaging of filters we read information as “up to 18,000 litres.” These guidelines generally refer to the volume of water without fish. If we study the product thoroughly we see that it is valid up to 7,500 litres with fish and 3,000 litres with KOI. So … of 18,000 liters we are very far away.

c) your own budget

Gravity filters are usually more expensive than pressure filters. If you opt for a gravity filter camouflaged in the ground, after having built the pond, excavation usually is very costly. 

Often appearances are deceptive: While being cheaper at first, the daily costs of a pump of a pressure filter may end up in unpleasant monthly electricity bills. Saving in the beginning – is expensive in the end.

In order to give an answer to “Which filter for my koi pond” let’s look now different to the types of filtration systems.


  1. pressure filters
  2. gravity filters
  • at the same water level as the pond
  • above the water level of the pond 

1. pressure filters

FullSizeRender 32_result

Pressure filters are filters that can be installed both – below and above – the water level of the pond.

They absorb water from the pond and pump it through the filter and again into the pond.


2. gravity filters  

a) at the same water level as the pond
 FullSizeRender 31_result

A gravity filter is a filter which is filled with water due to the principle of gravity. The great advantage of a gravity filter is that it does not require a pump as powerful as pressure filters as it does not have to suck the water to the filter.

Typical gravity filters have usually several cameras with different types of filtration material occupying quite a lot of  room.

A gravity filter is the best choice for medium and large ponds.


2. gravity filters 

b) above the water level of the pond 

FullSizeRender 33_result

Here we talk about a filter whose filtered water returns to the tank through the principle of gravity. The great advantage of a gravity filter is that it does not require such a powerful pump and pressure filters and – in this case – does not have to transport the water back to the pond.


Which filter for my koi pond ? With any filtration system you will find basic and sophisticated products. As we mentioned: There can not be too large filter. But there may be too small filter !!!!

The result is unhealthy water, koi diseases, green water and plenty of maintenance work which often takes away the desire to have koi.

The systems described above can be improved with a pre-filter before the filter (for the big pieces of dirt) and a sand filter after the main filter to filter even the smallest particles.

Recommendation: Most filtration systems come from northern Europe. There are complete sets including UV lamp … the set is then designed for the environment of northern Europe – so the power of the UV lamps is not enough for ponds in Spain (much less in the south of the Peninsula). We always recommend using the triple of what is recommended on the packaging of the manufacturers.