How to build a DIY pond filter in 8 steps

Pond maintenance doesn’t have to be a hassle. With a filter system in place, you can eliminate debris and unwanted particles and ensure that no unhealthy buildups stay in your pond. 

It doesn’t have to be costly, either. With this guide, you’ll learn how to make a DIY pond filter that works on small and large ponds. So prepare your materials, and let’s start!

What equipment and materials to use

You have flexibility in choosing your materials. For instance, you may choose a hose to connect the pump and the external filter (ideal for small ponds) or you can choose the sturdier option: PVC pipes. 

The following sections assume that you’ll use PVC pipes. Here’s everything you’ll need:

• Water pump
• Container with a lid (multiple containers are also okay)
• PVC pipe (take some measurements before buying)
• PVC cutter
• PVC cement
• Tape measure
• Bulkhead fittings or Uniseal to make a watertight seal
• A drill with different-sized drill bits
• A valve, plumbing elbows, PVC connectors, caps, and various fittings (will vary based on your project)
• Different-sized rocks (lava rocks or scoria)
• Cheap sponges
• Polyfill (optional)
• Anything that can create a void at the bottom of the filter (a large slotted pipe, old pots, etc.)
• A large bucket, basket, or terracotta pot for your pump to stand on underwater (very important!)

You don’t need to buy a new water pump if you already have one at home. If you do need to buy, make sure to check for quality and safety. Some pumps also have a “feed” mode that allows you to pause the filtering process during fish feeding times – perfect for a DIY koi pond filter! Also, if your pond has fish and water plants, check if your filter materials are safe for them.

Lastly, make sure to use a trustworthy container. The container will contain the lava rocks and other filter media, and you don’t want it to burst or leak. You can ask the nearest local hardware store for recommendations, but here are a couple of things to keep in mind:

• Use a container or multiple containers that can hold 10% of the overall pond volume (e.g., a 1000L pond will need a 100L container)
• The more and the larger pond fish you have (hence more fish waste), the more extensive filtration system is needed

Steps to make a DIY pond filter

1. Position the water pump and filter container in their ideal spots

Start by planning the filter system layout. Submerge your chosen water pump container or stand (a basket, a terracotta pot, and a plastic tub with holes on the lid would be good options) in the water, then place the submersible pump on it. This is a protective feature so that in case the filter container breaks and the water goes somewhere else other than back to the pond, the pump will stop drawing in water once the water level goes below its position’s height.

This will leave some water on your pond and keep your fish alive even when you don’t immediately see the damaged filter. Placing the pump inside a container (ideally, one that fits the aesthetic you like) would also make for a neater look.

After positioning the pump, set the filter container close to the pond – ideally in a shaded area. Make sure it stands on a level and sturdy surface. It doesn’t have to be right beside the pond, as long as you have enough pipes to run the distance between the pump and the filter. 

2. Drill holes in the container

At least two holes are necessary. One is on the lid where the pumped water will go in, and another is close to the bottom where the filtered water will flow out. You could also drill two or more holes for the outflow. 

Make sure the holes are suitable for your chosen pipes and bulkhead fittings.

3. Take the measurements

Use a tape measure to determine how many PVC pipes you’ll need to (a) connect the pump to your filter container and (b) create water outlet/s. This process should also give you an idea of what PVC connectors you’ll need and how many.

If you have a big pond, you’ll need a larger container or multiple average-sized containers for the filter. If you do use multiple containers, you’ll need a corresponding number of pipes to link each container to the main inlet pipe connected to the water pump. Consider all these as you prepare your materials.

4. Assemble the filter media

Get the container (or containers) and take off the lid. Inside the container, gather the filter materials while carefully leaving as much air space at the bottom as possible for the filtered water to flow out smoothly.

You can start by placing some slotted pipes into the container (to create voids and air space) and then the lava rocks. Be careful not to block the holes for the water outlet (you can already position the outlet pipes with Uniseal to help with this). On top of the rocks, lay the sponges followed by layers of polyfill. You could also use laundry bags and a metal screen as alternative or additional filters. Put the lid back once you’re done.

5. Install the pipes

Time to connect everything! Position the PVC pipes in their appropriate places, then connect them using plumbing elbows or other fittings. Don’t seal them yet – do that later after doing a test run!

For the pipe that goes into the container lid, it’s a good idea to connect it to another horizontal pipe (which should rest above the filter media and under the container lid) with multiple holes for the water to go through. This will distribute water evenly and prevent the water from going through the filter too strongly.  It also helps slow down the water flow and allow it to have contact with the beneficial bacteria on the lava rocks.

6. Do a test run

Connect the pump to a power source and test if your DIY project works! You’d want to see water leakage from some of the pipe connections (a good sign that the water is flowing through) and water flowing out of the container and back into the pond.

If water doesn’t come out of the container, check if there’s enough void between the filter elements or if the outlet pipes are blocked. Fix until the water circulation is right.

7. Seal the pipes

Once you’re sure the filter system works fine, cut the power off and start sealing the pipes using PVC cement or any fish-friendly sealant. Remember not to cement the pipe on the filter container’s lid – the lid should stay removable so you can clean and replace the filter materials as needed.

Give the PVC cement at least 2 hours to dry, or however long the manufacturer prescribes. 

8. Turn the power on and watch your DIY pond filter do its job!

Finally! You can now have peace of mind that your pond will stay clean for longer

With the pond filter working smoothly, you can also consider disguising or beautifying how it looks as part of your overall pond landscape. Having a mini-rockery garden around the filter system might be a good idea. You could consult a gardener or a garden designer if you like.

Aquatic plants and marginal pond plants would be great, too. Plants like Louisiana irises, canna lilies, and rushes are best to create a ledge. Just try to avoid plants with roots that penetrate the area where solids accumulate.

A small pond filter system can be an excellent spot for lettuce, mint, strawberries, or anything else where roots can be constantly wet.

More tips to beautify & maintain your pond filter

Congrats if you were able to build a DIY pond filter! That should make pond maintenance a lot less stressful, and you can now enjoy the view without dreading the next pond cleaning session.

If a DIY method isn’t really an option, you can always ask a Tasker to help you out. Just be specific with your request (Should they buy the materials? Will they need to clean your pond first? Do you need them to disguise the filter system with plants or other garden decors?)

You’ll eventually have to think about filter maintenance as well. As needed, hose down the filter media and check if anything is due for replacement. Doing so will keep your filter system in good condition – and your pond ecosystem too!