Happy Koi Koi Pond Filtration

How to filter your Koi pond from start to finish - what you need to know.

Successful Koi keeping is easy. Watch what successful people do, and do that!

When it comes to Koi pond filters, the philosophy is no different.

If you think about your Koi pond there are several critical success factors that make or break filtration systems. They also make or break your ability to enjoy your Koi pond!

In our minds, based on many years of experience and observations of thousands of filter systems, the best filtration for a Koi pond is a system that absolutely has to:

    1. be easily flushed of solids in two to three seconds, preferably daily.

    2. provide massive biological performance

    3. use as little power as possible

    4. be as flexible as possible so that you can upgrade or change at any time

There are many systems that claim to achieve all this and we can count on the fingers of one hand the number that can actually deliver it.

In order to achieve all of the above, an open filtration system is the only design that can work. By 'open' we mean low pressure - i.e. filters that you can access whilst they are running. These are very different to closed box sand filter/bead filter/black box bio filters that cannot be opened when running without you getting very wet indeed!

Think of your Koi pond filter as a black box. Water from the Koi pond enters this black box, is filtered and cleaned, and returned back to the Koi pond, using as little effort as possible.

A Koi pond filter system is NOT a sand filter followed by a bio filter followed by a U/V light all powered by an energy guzzling swimming pool pump despite what anyone may be telling you. Be wary of such claims - these systems will come to represent colossal costs to you in the future - we guarantee it!

The trouble with them is that they are easy to install and to walk away from. This makes them popular amongst Koi pond builders who really have only the next project on the horizon as their interest. There is no thinking involved: simply cut, glue and walk away.


In a Koi pond, your Koi basically live in an open toilet. It's not pleasant to think about, but that's the cold hard truth of the matter. In a Koi pond, solid waste material and dissolved waste material are your constant battle and the forefront of what your filter system should be dealing with.

Solid waste material comprises of obvious things such as Koi poop and dead algae but there is plenty more. Mulm and sludge build up come from dead bacteria, insect larvae, leaves, dust - you name it. In a Koi pond there is a lot of it and it is your mechanical filters that deal with this waste load.

Dissolved wastes are primarily the ammonia that Koi excrete directly into the water from their gills. It is your biological filters that deal with this waste material.


1. Easy flushing of solids, preferably daily.

Solids build up in a Koi pond should be removed as often as possible, preferably at least daily. Solid debris in a Koi pond if left within the environment (and this includes your mechanical filters of course) it rots and breaks down into all sorts of nasty substances. In short, solids go rotten rapidly and they are not a good thing to have floating around in either your pond, or the filters.

Any good mechanical filter will be able to collect all the solids together in one convenient place to allow them to be easily flushed, quickly and daily. No sand filter or bead filter can do this for you as these require a full back wash cycle to achieve any solids removal which can take anything up to 20 minutes.

gULP on Stand

The gULP filter system answers all the needs of a Koi pond filter

We've dealt with this issue in gULP - our filter system designed to specifically give you the best in Koi pond filtration. gULP when fitted with brushes as a mechanical filter allows the accumulation of solid waste material into the square sump located at the bottom of the filter.

All that is required is to open a flushing valve for a few seconds once a day to purge all the solid wastes from your Koi pond. Note that if you miss a few days (or weeks), gULP will not fall over and suddenly cease to operate. Solid material will continue to accumulate of course, but the filter will continue to work.

gULP Interior

Interior of gULP showing brush pole support slots and sump at bottom of filter


gULP Filter with brushes installed

gULP with brushes installed

You can see that gULP ensures that the brushes are packed equidistantly apart with the correct brush density to ensure sufficient overlap.

Once installed the brushes need only be removed on special occasions. They can be easily cleaned from above by simply hosing them down and do not need to be removed and hosed down individually.

gULP allows you to flush all the solids from your system quickly and easily in a manner of seconds.

2. Massive biological performance

The second thing that gULP allows you to achieve is truly monstrous biological performance. gULP is specifically designed to accommodate ANY type of filter media - the unit can accommodate upto three stainless steel trays internally onto which any media can be packed.

Our preference is for the use of SuperActiFlo - the moving bed bio media. This is simply because SuperActiFlo has so many distinct benefits over conventional media. These include:

1. It's self cleaning

2. Near perfect mixing within the turbulent moving bed environment the increased mixing ensures no water can possibly track from one end of the filter to the other (tracking occurs in all static media and can ensure up to 85% of static media is effectively inactive) meaning all SuperActiFlo is at work, all the time. This can improve performance over static media by upwards of 500% to 1000%. Yes, you read that right!

3. Oxygen rich water is returned back to the Koi pond.

4. SuperActiFlo is a zero head loss bio filter.

5. Continuous bio film renewal within the moving bed enhances bio filter performance further.

SuperActiFlo moving bed bio media virgin material  SuperActiFlo moving bed bio media recycled material

SuperActiFlo now available in white (virgin material, cheap) or black (recycled material, cheapest) flavours.

The choice is up to you. gULP can handle truly massive quantities of bio media, allowing for massive biological performance from your media of choice.

3. Uses as little power as possible

gULP has been designed to take the best of all worlds from existing filter systems to provide you with maximum flexibility and maximum benefit. This is possibly best summed up when gULP is installed appropriately the filter can be powered with something as small as an aquarium power head. These can provide water movements of 10kl/hr at just 26W of energy consumption!

Efficient pumps suitable for gULP in a low power environment range from pumps that consumer just 90W and deliver 18kl/hr (at very low head) through to pumps rated at 175W for 14.8 kl/hr (12kl/hr at 1m head, 10kl/hr at 2m head). Pumps can be installed internally in gULP or externally depending on your choice of pump option.

Compare these with swimming pool pumps that are typically rated at 750W or 1100W and the energy cost difference both monetary and environmentally are staggering.



4. Flexibility

We've mentioned gULP is flexible. gULP can be used as a gravity fed pump return system (for maximum power advantages). It can also be run quite happily as a pump fed gravity return system.

gULP is installed using nothing more than a hacksaw, a screw driver and some PVC glued pipework.

gULP is completely customisable to suit any installation requirement. Multiple gULPs can be run in series, or in parallel, or in any combination of these.

gULP can be scaled up to suit any size Koi pond - and it can be changed at any time you want to change it. Infinite combinations are possible - although you may not ever explore all of them gULP will allow you to fine tune your system to work exactly the way you want it to work for you.

gULP can be installed flexibly on any of it's four flat sides. Flush or drain pipes can also be accommodated in any direction. gULPs can be installed in long lines, or in square configuration.

gULP is self supporting. All it requires is a stable base on which it can be mounted - optional stands are available for this purpose. gULP can stand on bricks if need be - and once filled with water gULP will not warp or lose shape over time.

Internally gULP can be configured to run as an under over, sideways through or top down system. Optional stainless steel plates will allow you to accommodate any bio media. Void spaces can be created and gULP can even be run as a bakki shower should you require it.

And of course gULP is priced extremely competitively. We think you'll be pleasantly surprised at the costs when compared to other proper Koi pond filter systems although we believe you'll need to spend up to three times as much to get the same performance!


We firmly believe that gULP has it all. It's the product of years of testing, experimenting and proving the technologies behind Koi pond filtration. gULP incorporates the best of the past and the best of the future in one easy to use and easy to understand system. 


Lastly, we built gULP for you, the Koi keeper. We also know that your Koi will thank for you using it.

Check out the forum for examples of installations as they happen, and ask us questions directly..