Pond Filtration

Pond Filtration: Keep Pond Water Clean And Crystal Clear

In a closed system like a garden pond, an effective and efficient filtration system is essential. There are lots of different ways to filter your pond's water and, by extension, keep your fish happy and healthy. The best way is, of course, with a dedicated pond filter filled with porous filter medias. We stock a wide range of pond filters, filter medias, and associated accessories here at Swell UK, suitable for all types of garden ponds from small wildlife ponds to large Koi ponds. This range includes some top brands in the pond keeping hobby, such as Evolution Aqua, Hozelock, and Oase, as well as our own outstanding range.

What is a pond filter?

A pond filter is a piece of equipment designed to remove waste products and excess nutrients from your pond's water column. There are lots of things in a garden pond that can produce waste and promote nutrient build-up, from fish to decomposing plant material. If left unchecked, this waste can accumulate, rot, and slowly but surely poison your fish. It's a pond filter's job to remove this waste, break it down, and maintain clean and crystal clear water year-round.

How does a pond filter work?

A pond filter works by forcing 'dirty' water through a series of filter medias, e.g. sponges, ceramic rings, porous rock. This process physically removes waste particles from your pond water (mechanical filtration) and, courtesy of the beneficial bacteria that live inside the filter media, breaks them down (biological filtration). The large colonies of beneficial bacteria that live inside your filter feed on excess ammonia and nitrite, turning it into nitrate. This nitrate is readily absorbed by pond plants as they grow and, in turn, effectively removed from your system.

What pond filter do I need?

There are lot of different types of pond filters to choose from, and they all differ in shape, size, form, and function. While each filter has its own unique strengths, and weaknesses, all will help to improve water quality and clarity. The model you ultimately choose will also depend on the size of your pond and the strength of your pond pump. It's best to work out the size of your pond (using our handy pond volume calculator) prior to choosing your pond filter. Here's a quick breakdown of the different types of pond filters for sale on our website and how they work:

• Pressure Filters - these pond filters keep water pressurised, meaning they can be used alongside water features that require water to be pumped above the water level of your garden pond. They have large filtration capacities and several models, including our Swell Pressure Filter Premium, come with internal cleaning mechanisms that stop them from getting clogged with waste.
• Box Filters - these pond filters are also known as flow-through pond filters and rely on the force of gravity to force dirty pond water through a large box full of filter medias. They have huge filtration capacities, often with extra space for you to add even more filter media. They're also easy to maintain and don't need to be clean quite as regularly as other alternatives.
• In-Pond Filters
• Koi Pond Filters

Some garden ponds require additional forms of filtration. On top of a pond filter, a suitably sized garden pond stocked with lots of fish may also require a UV clarifier and/or a pond skimmer to maintain clean and crystal clear pond water. UV clarifiers stop algal blooms in their tracks and neutralise any stray pathogens or viruses living in your pond water, while pond skimmers filter the top layer of your pond and keep its surface free of debris and scum. Both make fantastic additions to garden ponds, not only by boosting their overall filtration capacity, but by providing benefits that other pond filters aren't capable of providing. Some pond filters come with built-in UV clarifiers, removing the need for you to invest in additional equipment.

Does every pond need a pond filter?

Not every garden pond requires a pond filter; wildlife ponds, for example, don’t typically house fish so there’s no real need for a filter to remove and break down waste. A Koi pond, on the other hand, requires a substantial pond filtration system to ensure a healthy environment and one that’ll support a growing population of large Koi carp.

Can you over-filter a pond?

As a general rule of thumb when it comes to pond filters, bigger is always better. There’s no such thing as ‘over-filtering’, so if you have the budget and ground space for a larger and more powerful filter, always go for the bigger option – your fish will thank you! Aside from in-pond filters that typically stay small and are only really suitable for medium-sized ponds, pressure filters, box filters, and Koi pond filters all get pretty large. The biggest models amongst these ranges of pond filters are powerful enough to effectively filter huge ornamental ponds full of fish.

That said, not every pond keeper has the budget for a big and powerful filter, nor the need if they have a wildlife pond or a small pond with very few fish. If you’re one of these pond keepers and you’re after a filter that’s perfectly tuned to the size of your pond, then you’ll want to select a filter that has a capacity that matches the volume of your pond. You’ll also want to partner this filter with a pond pump that’s capable of turning over the total volume of your pond at least once per hour.

For more advice on how to choose the right filter for your pond, check out our handy help guide on the topic here.