Pond Filtration

A must for every pond owner is pond filtration. Having a filter equals happy fish and clean water so you can admire them.

Now when it comes to filtering a pond there are a number of different ways to do it – but the principles are the same.

When investigating filters for your pond you will hear plenty of terms like biological filtration, filter media, nitrogen cycle, turnover per hour, etc, etc, etc.

What you need to understand is which pond filtration system will work for you because they are all different and perform in different ways.

As a new pond owner, you are most likely going to use some sort of mechanical/biological filtration that provides a home for beneficial bacteria. These beneficial bacteria live in the filter system and feed of the ammonia and nitrites produced by your fish and dead plants in your pond.

A mistake we often see is that the owner thinks everything is ok because the water is clean. But clean doesn’t mean safe. There could be high levels of ammonia in the water and you would never know. Filtration is a must for a healthy pond.

Pond Filters 101 – How does a pond filtration system work?

Let’s take a quick look at the various options available. Ponds come in all shapes and sizes and pond filtration is no different. Each system runs different filter media

Pressure Filter

Probably the most popular pond filter and easiest to manage is a Pressure filter. These filter systems provide plenty of surface area in a pressurized canister that is fed by a pump in your pond. Both mechanical filtration and biological filtration occurs in these types of filters. They may have a couple of layers of filter matting that work as mechanical filtration to screen out larger particles and a bunch of bio balls that work as a biological filter to harbor good bacteria that feed on ammonia/nitrite and turns it into good nitrates.

There are easy to set up and most kits now come with a pump, pipework, and all the fittings you need to get the filter up and running quickly. Some even have a UV clarifier included that will help with green pond water and algae blooms that turn your water a pea-green color.

When it comes to positioning your filter setup you have quite a few options with a pressure filter. Because the water is pumped into the filter directly from your pond it remains under pressure so the filter can be below water level. This comes in handy if you want to hide or partially bury the filter and just have a return hose going back to the pond or waterfall or other water features if you are lucky enough to have them.

Gravity Return Filters

Next up we are going to take a look at gravity return filters. As the name suggests these types of filters return the water back to your pond with gravity. The filter outlet needs to be above the water level for them to work properly.

A great use case for a gravity return filter for ponds is to have one as part of a waterfall. You often see these in water gardens with rock waterfalls. There are numerous benefits to this setup:

The noise of running and splashing water is very relaxing

The return water helps oxygenate the water

Water movement can help push floating debris towards a skimmer if you have one installed

If you have not yet planned a waterfall into your pond then you often see these filters sitting alongside ponds with the exit spout hanging over the water’s edge.

This is ok in the short-term to get your filter system up and running but you are going to want to hide it at some stage so plan ahead if you can.

Gravity Fed Filters – How do I filter a large pond?

On larger ponds, you will often see gravity-fed filters in action. These are a far more complex filter for a pond and keep your pond in perfect shape, especially if you have Koi who need really good water quality for the pond ecosystem – but at a cost…

For a start, you need to install a bottom drain at the bottom of the pond. This drain feeds the system via a 4″ pipe from under the pond and gravity forces the water along the pipe and into your system. Once the top of the filter is just above the waterline of your pond the water will flow into your filter via gravity.

Within the filter itself, you will have several different chambers containing filter media allowing for a large surface area to grow bacteria. This may be filter mats, Bio Balls for biological filter processing, and an empty settling chamber so the solid waste will drop out of the pond water.

You will need to pump somewhere in the filter for pond filtration to get the water back to your pond once it has been through the filtration process and because you are using a pump you have plenty of options for water return to the pond.

You will see TPR’s on the inside walls of larger ponds. Tangential Pond Returns are used to direct the water flow towards a pond skimmer or to cause a circular motion to aid the bottom drain in removing solids and waste from the pond floor.

In terms of cost, the gravity-fed systems will be the most expensive if you go for the full setup.

Bog Filter – How do you naturally filter a pond?

If you have the space available you could consider a natural bog filter for your pond. There is no real mechanical filter processing here but the idea is that you create a bog for plans

Different types of pond configurations call for different filtration systems but these are the main types of filters you should consider when building a new pond.

A filtered pond is a healthy pond and a bog will prove to deliver quality water for a long time without too much maintenance once it is setup.



It’s basically a contained tank with a grid or rocks and gravel separating the water from the bulk of the pond plants. The water is pumped into this gravel area and the roots of the plants hang down into the water and draw up all the nutrients that cause problems in your pond. These roots have a great surface area one the plants have established and that alone can keep your pond in perfect condition.

The one downside to a bog setup is that it can take a long time to establish so you may want to substitute the filtration until everything is established.

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