Diy pond filter

For me having a pond or water garden is one of life’s essentials.

I love nothing more than coming home from work and grabbing a cuppa to sit by the pond and watch my Koi and Goldfish swim about.

Having a koi fish pond can be an expensive hobby though so today I’m going to go through step by step how I built my own DIY pond filter system.

From picking the right kit to putting it together and getting it up and running.

First, let’s look at why you even need a pond filter.

my diy fish pond filter

Water that sits still for long enough will stagnate. Add some fish to this water and things go bad really quickly.

The best way to keep things healthy and keep your water crystal clear is to add in some sort of pond filtration.

One of my koi ponds is about 800 gallons and I use it for smaller fish. When I was building the pond the plan was always to make a homemade pond filter system to keep the pond water clean.

Filter systems come in many different shapes and forms. From a natural bog filter to a shop-bought pressure filter, or even a DIY pond filter.

That’s what we are looking at today. This is my diy pond filter system, so let’s get into it.

DIY koi pond filters

This is a 3 stage koi pond filter and the bio filter system uses K1 filter media. Each filter container is roughly 15 gallons. Plenty big enough for most backyard garden ponds.

So let’s have a closer look at what you need to put this awesome pond filter together.

Barrel Filter Setup

The first barrel will be used as a settling chamber to remove most of the larger fish waste. The second will contain K1 filter media and run as a static bed to filter smaller particles out of the water. You could also use bio balls or lava rock in this chamber. The water is pumped from the pond into this pond filter system.

The third barrel also contains K1 media but will have air stones added to run as a moving filter bed. The water is then gravity fed back to the pond.

You can pick these plastic drums up all over the place including here or try asking around local food producers.

barrels for pond filter system

Pipework & Fittings

For this pond filter, we are using a mix of 2 inch and 1.5 inch PVC pipes and fittings. You will need the following:


  • 5 meters of 2″ pvc pipe – solvent weld
  • 4 meters of 1.5″ pvc pipe – solvent weld

Fittings 2″

  • 9 x 2″ 90° bends
  • 5 x 2″ tank connectors

The 2″ pipes and fittings are to connect the water feed from each barrel with the tank connectors and also for the outlet back to the pond.

Fittings 1.5″

  • 3 x 1.5″ 90° bends
  • 4 x 1.5″ tank connectors

The 1.5″ pipes and fittings are for the drain system to help clean out the muck from the bottom of each barrel. There is also a bulkhead connector for one of the barrels to connect up the feed from the pump.

The only other things you need to complete this pond filtration system is a drill with a 2″ and 1.5″ hole saw and a 5/16 drill bit, a hacksaw or hand saw, a measuring tape, a few other household tools, and a tub of PVC glue. You don’t need to be a diy expert to build this filter system.

The base for the filter.

With this type of pond filter, you need to allow for drop off in water between barrels so from left to right sit the first barrel flat on the ground.

Create a 4″ step up for the middle barrel and then add another 4″ for the third barrel. There is lots of information online about water flow and drop-off rates but this is what works for me and my garden pond.

This way when the water starts to flow through the filter system the levels will be roughly the same across all 3 drums.


Now that you have all the kit you need let’s take a look at how this all goes together.

We will start with the barrel nearest the pump.

Barrel 1 is the first stage of our filter system. It has the pump feed inlet and a single 2″ exit to barrel 2. There is also a 1.5″ drain for cleaning.

This is the barrel that catches most of the heavier solids from your pond. Many people avoid adding any filtration media to this stage of the filter and have the water enter the filter in a swirling motion. All DIY pond filters are different so you can choose what you would like to do here.

For me, filter systems should be able to handle a heavy fish load so I want as much media as possible to keep my water crystal clear. I have a variable pump that can push upwards of 1800 gallons per hour and because koi ponds can get very dirty the more filtration I can squeeze into a filter, the better. 

Right, first thing to do is measure down about 8 or 9 inches and cut your first 2″ hole for the outlet pipe.

Use a file, knife or sandpaper to remove all the burrs from around the edge of the hole.

It’s also a good idea to tip your barrel on end once the holes are drilled to empty out the burrs and bits of plastic that drop into it otherwise you will forget and they will end up floating in your pond later.

Next, you want to fix your first 2″ bulkhead connector.

Keeping the smooth side out slide on a washer and push the bulkhead into the hole.

Reach in and screw on the retaining nut.

Leave these loose until you have all the pipes connected but remember to tighten them up after to avoid any leaks. 


how to fit a bulkhead fitting
backyard pond filter diy

Next, you need to add the inlet for your pump. For this, we use a 1.5″ bulkhead connector and a matching hose tail fitting.

Remember this is a 1.5″ hole so make sure to change your hole saw bit.

It’s the same process to fit the bulkhead fitting but you can tighten this all the way.

There is one more 1.5″ hole to be drilled for the waste drain.

Measure up about 4″ inches or so from the base of the barrel and drill a hole and fit another bulkhead connector.

This will be used to drain the muck out of the bottom of the barrel when cleaning.

adding pump connector to pond filter

Now that you have all your holes drilled in Barrel 1 it’s time to start adding the internal pipework.

This is very straightforward.

Let’s start with the 2″ outlet pipe. 

You want to have a pipe facing upwards roughly in the middle of the barrel so measure out from the bulkhead to the centre of the barrel. You need to allow for the extra 1.5″ pipe fitting into the bulkhead and the addition of a 90° bend.

Once you have this fitted – dry fit – you can add another piece of 2″ pipe pointing upwards towards the top of the barrel.

inside a diy pond filter

vertical pipework inside barrel one of my homemade pond filter.

I used a spirit level flat across the top of the barrel to measure down to the inside edge of the 90° bend and subtracted an inch to be safe.

Push this pipe down into the 90° bend and measure up about an inch or so and mark a line. Measure down about the same from the top of the pipe and mark another line.

You are going to need to drill a series of 5/16 holes into the pipe between the lines to allow for the water to drain out into the next barrel.

You might look to install some course filter matting in this chamber to remove some of the heavy waste that doesn’t sink to the bottom of the DIY vortex filter.

Now that you have Barrel 1 nearly ready let’s move on to Barrel 2.

Barrel 2 – Middle

With Barrel 2 you have water coming from the first barrel and you have another outlet that goes to barrel 3.

First, measure down 9″ from the top of the barrel and drill out a 2″ hole and fit your top bulkhead.

Next, you want to measure up 9″ from the base of the barrel and drill a second 2″ hole for the bottom bulkhead.

Make sure to keep these 2 holes lined up on the vertical.

Now you can also measure up 4 inches from the base and drill out a 1.5″ hole for your waste and fit the bulkhead fitting in place.

The internals of the middle barrel is similar in some ways to barrel 1. 

The top pipe is the same – just be sure it’s centred to the barrel and leave an inch from the top for overflow.

You can use the same measurements for the bottom internal pipe but this time point the 90° bend down towards the base of the barrel. This will help with circulation.

For the waste pipe, you can cut a length of 1.5″ pipe and drill a load of 5/16 holes all along it. This will help drain the waste later on.

This barrel will be used as a static bed, and in our case, we will be adding a large bag of K1 media to it.

There are no air stones required here as the water flow is enough.

With that work completed, it’s time to move on to the final stage of our bio filter setup. 

Barrel 3 – Moving Bed Filter

The final barrel in this setup is barrel 3. 

There is only 1 2″ inch inlet in this drum so measure up 9 inches from the base of the barrel and drill a 2″ hole and fit a bulkhead.

Measure up 4 inches from the base and drill a 1.5″ hole and fit a bulkhead fitting for your waste.

Now you need to spin the barrel 90° and measure halfway up the side and drill another 2″ hole and fit a bulkhead. This is for the 2″ pipe that flows back to the pond.

The internal pipework for this drum is the same measurements and the bottom pipe in barrel 2 but this time you are going to point the 90° bend upwards.

As this is a moving bed filter the additional turbulence of the water helps keep the filter media moving about.

Connecting everything together.

We are nearly there…

The next thing you need to do is add the external 2″ pipes and connect the barrels together.

First cut 4 x 4″ lengths of 2″ pipe and push these into the bulkhead fillings in each barrel.

Next, you need to push-fit the 90° bends onto each of the 4″ pipes you just added.

You can see from the pictures that they are all angled 45° either point upwards or down.

Measure between each barrel (allowing for the extra pipe that slots into the 90° fittings on both ends) and cut 2″ pipe to suit.

my diy fish pond filter

Final Assembly.

Once you are happy with how everything fits together you can break out the PVC cement and start gluing it all together.

Start with the short external pipes into the bulkheads, then add the 90° bends one at a time.

Next glue in one end of the connecting 2″ pipes, let it set, and then repeat for the other end.

Continue on for each barrel.

When this stage of your filter setup is completed you can glue the hose tail connector into the 1.5″ hole in the side of Barrel 1. Attach your flexi-hose from the pump and that is barrel 3 completed.

Move now to Barrel 3 and glue in the 2″ external pond return pipe into the bulkhead on the side of the barrel.

The last thing you need to do is fit the external pipes and ball-valves for the waste outlets. 

DIY Pond Filter – Pond Pump Setup.

I was lucky enough to install a bottom drain in my pond when I built it and due to the layout of the pond, I can get water back to the base of the filter platform via gravity.

I have installed a new dry pump to pump the water up into the pond filter system.

This is a great pump and I’ll write a review up on it another day. Whisper quiet and plenty of power. Plus it has a variable control so you can adjust the flow to suit your filter setup. Find out more about it here.

The water goes back into the pond via gravity.

If you have gotten this far then well done. You now have a bio filter system for your pond that can easily handle all the waste you fish can produce and keep your water crystal clear.

Barrel 1 – Vortex or Static Filter

inside a diy pond filter

If you are using this as a vortex filter then turn the 90° bend to the right so the incoming water swirls around the barrel. This will cause the waste to drop out of the water column and cleaner water will rise up the filter and through the outlet into barrel 2.

Barrel 2 – Static Bed Filter

inside a diy pond filter

This is a static bed – where the filter material is used to remove more of the solids from the water. add media to cover about 30-40% of the volume of the barrel. This is where your good bacteria will start to colonize and eat the waste from the water.

Barrel 3 – Moving Bed Filter

inside a diy pond filter

In this barrel, we are using a couple of airstones running from a small air pump. The addition of oxygen into the filter material here really helps the beneficial bacteria to grow and clean the last waste out of your water. Add one of these to your garden pond and your fish will love it.

During the summer months, you may start to get green algae growing in your pond. This filter is great at removing fish waste and muck from the pond but algae is a different problem altogether. For this, you may need to introduce uv clarification to help kill this off. It doesn’t do any harm to your fish but to get the best out of your pond filtered water through a UV light will keep everything clear. Check out our UV lights review.

If you have a backyard pond, a water garden, or even an aquaponics system then one of these filter systems will be perfect.