Submerged DIY Pond Filter

How to Make a Submerged DIY Pond Filter

I'm not just into tech gadgets, but also have a keen interest in decorative fish and ponds. Roughly 15 years ago I got my very first pond, however, is not a traditional garden pond seated in the ground.

Instead, it's a premade treated wooden raised pond complete with liner that you slot together. It's great because you don't have to dig a big hole and shift tons of unwanted soil around your garden. In fact, the only preparation you have to do is build a basic base with patio slabs or concrete.

However, the problem with a raised wooden pond is trying to incorporate a pond filter. For 12 years I just had a normal filter box, which was propped up on several breeze blocks which looked unbelievably ugly.

3 years ago I replaced my original wooden pond with a new one since it was looking tatty. I really, really didn't want the same setup when it came to the filter so I got my thinking cap on. After a few days I came up with the idea of making my very own underwater/submerged pond filter. I wasn't really sure whether it would work, but since the cost was fairly low, I went ahead.

The good thing about an underwater/submerged pond filter is that it would be completely hidden within the pond. Sure, you would lose some pond space, but since the aesthetic looks would be 1000 times better, it was a small price to pay.

The filter I made is both a biological and mechanical filter, though it won't clear green water.

To make the filter I used the following:

  • 1. Drill with a drill bit that can drill holes approximately 1 inch in diameter.
  • 2. 2000 L per hour pond pump.
  • 3. 25 L bucket with sealable lid and plastic or galvanised handle.
  • 4. 2 small bricks.
  • 5. Biological filter media consisting of plastic hoops, which was taken from my old filter.
  • 6. Nylon pan scourers, which would act as both a mechanical and biological filter media.
  • 7. 2 meters of 22mm PVC waste pipe to connect to the pump.
  • 8. 22mm 90 Deg Tee
  • 9. Small hacksaw to cut the PVC pipe.

Since I already had a drill, pump, hacksaw, plastic filter media and a couple of bricks, the only things I had to buy was the bucket, pan scourers, 22mm PVC pipe and 90 deg tee, the cost was very minimal. If you had to buy every item, then the cost would be fairly high and probably not worth it, since you could buy a premade underwater filter for a similar price.

I should also point out that the 25 L bucket and filter media was calculated on my pond size (350 gallons) and number of fish (approximately 15 large goldfish varieties). You may need a smaller or larger bucket and filter media volume depending on your pond size and fish numbers. I also made sure that the bucket was big enough to accommodate the pump and that the pump outlet fitted the PVC pipe (i.e. 22 mm).

How to Make the Filter

Before you begin, you should ensure that your pond has a has a flat base, unless the pond filter will not sit level. Also make sure that your pond is of an adequate depth that the bucket will have at least 5 inches of water over its lid once submerged in the pond.

First step once you have your bucket is to drill a series of holes in the lid. Ideally make these holes nice and big, roughly around 1 inch in diameter. This allows the water to flow through freely and allows gases to escape. Also make sure you drill a hole in the centre or cut a square hole with a knife. This is for the PVC pipe, which will be connected to the pond pump.

Series of large holes drilled into the top of the lid

Next step is to place your pond pump in the bottom of the bucket. The bucket I used had a slight ridge in the centre so to ensure that the pump stayed level i placed 2 washing-up sponges on the bottom and then sat the pump on top of them.

Pond pump placed in the bottom of the bucket

At this stage, you also want to make sure that you thread the pump cable through one of the holes in the lid before you wire it up to the junction box permanently or attentively, you can cut a groove in the side of the lid.

Pond pump cable threaded through one of the holes in the lid

You now want to place 2 small bricks either side of the pond pump. This will help to weigh down the filter, once it's placed in the pond.

2 small bricks placed in the bottom of the bucket to weigh it down
Before you add any filter media make sure you connect the PVC pipe to your pond pump. Once that's done you can then start to fill the bucket with a biological filter media such as plastic hoops. You're free to use any filter media you like, but please make sure it's light and that water can easily flow through it. If you use something like gravel, it will be far too heavy and likely to damage the pump. I filled the bucket, roughly halfway with plastic hoops. If you know the exact depth of your pond you can also cut the PVC pipe so it sits roughly 2 or 3 inches above the water surface at this stage. If not, do it later.

Plastic filter media added to the bottom of the bucket

We can now add the final layer of filter media. For this, I'm using pan scourers, which will act as both a mechanical and biological filter media. You can buy these from supermarkets or general household shops. These will last for years and years and the only drawback is that they are buoyant, so you have to make sure you have enough ballast in the bottom of the filter (i.e. 2 bricks) to stop the filter floating. When you fill the filter with pan scourers, I would leave a small gap of 2 inches from the lid of the filter as this allows them to float around and helps prevent clogging.

Pan scourers added to act as a mechanical and biological filter media

Once your bucket filter is full of filter media, you can now place and seal the lid on.

Fitting the PVC pipe to the pump

The final step before you place the filter in the pond is to connect 2 pieces of the 22mm PVC waste pipe to the 90 deg tee and connect it to the pipe coming from the pump. Ideally, the 2 pieces of PVC pipe coming from 90 deg tee should be slightly longer than the filter itself as this helps to distribute the water evenly around the pond before it re-enters the filter. As previously mentioned, if you don't know the depth your pond you can place the filter in first and then make a mark on the PVC pipe and cut it to the appropriate height, ideally 2 or 3 inches above the water surface.

Connecting the T piece and 2 further pipes to complete the filter

To place the filter in the pond, you simply push it down in the water until all the air escapes and it settles on the bottom. You can then turn the pump on and the water will be drawn through the top of the filter through the filter media and out through the PVC pipe.

The DIY pond filter completely submerged and operating in a submerged pond

How Do You Clean the Filter?

I've been asked a few times about how easy this filter is to clean and the answer is fairly simple. All you have to do is leave the pump on and gently pull the filter bucket upwards until the pump pumps all the water out. You can then lift it out of the pond turn the pump off and clean the filter media, ideally in pond water, as tap water can kill the friendly bacteria. The process should take you no more than 20 to 30 minutes, once you get used to it. I clean mine roughly every 6 weeks during the spring, summer and autumn months. I generally don't run the filter through the winter months, unless the weather is very mild.

You can watch a YouTube video of me making this filter over 3 years ago. Since then I have made small alterations which are reflected in this guide.