How to choose a pond filter and UV

All pond keepers want clear water and healthy fish, and a good filtration system is the key. There are many different types of filtration units, all perfectly suited to different needs, pond types, and stocking, which may seem a little daunting to choose from. In this guide, we will explain the features of each filter, from box filters to large systems, and how UV clarifiers help keep your pond water clear.

Recommendations:

• Small, low stocked ponds: All-in-one filters are simple and easy to set up.
• Small to medium ponds: Choose a box filter for budget friendly filtration.
• Medium ponds with higher fish stocking: Use a pressure filter for flexibility.
• Large, well-stocked ponds: Invest in a gravity fed Koi Pond system for maximum waste handling.
• Green water problems? Add a UV clarifier to your system to eliminate floating algae.

Tip: Always size up when selecting your filter, you can't over-filter a pond, but you can under-filter.

Our top picks:

• Swell Pressure Filter Premium: Features built in UV, large mechanical and biological filtration capacity, and an internal filter foam cleaning mechanism.
• Blagdon Inpond All In One: filter, pump, and clarifier with LED lighting and fountain heads. Perfect for small-large ponds.
• Oase FiltoClear: Combines mechanical and biological pressure filtration with UVC technology for clear pond water.
• Evolution Aqua EazyPod Complete UVC: mechanical, biological, and UVC filtration for large Koi ponds.

Box Filters: Simple, yet effective

Box filters are one of the most common choices for pond filtration, especially for small to medium ponds. These systems are large containers that allow plenty of room for sponges and biological media. A pump is used to push water into the box, where it is filtered through the media and returned to the pond by gravity.

These units are highly effective at trapping waste, as well as housing colonies of beneficial bacteria that break down ammonia and nitrates. Some units even feature a built-in UV clarifier, but others may require a separate unit to handle green water.

Pros:

• Quick and easy maintenance: simply lift the lid and clean the sponges with pond water
• Typically affordable and suitable for a wide range of small to medium ponds
• Media can be upgraded: you may want to swap out for carbon or zeolite

Cons:

• Large, bulky units that can be challenging to keep discreet
• Must be positioned above the water return point, such as the top of a waterfall

Ideal for: Small-medium ponds built on a budget with a modest amount of fish.

Pressure Filters: Compact and versatile

Pressure filters are sealed canisters that typically include biological and mechanical media, often featuring a built-in UV. In contrast to box filters, water exits a pressurised filter under pressure, which means it can be pumped to higher elevations, making it a fantastic choice for waterfalls or distant water returns. You can even keep your unit discreet, burying it partially to avoid obstructing the view of your pond.

Pros:

• Can be kept hidden
• Can be positioned at ground level or next to waterfalls
• Some models include an easy clean feature

Cons:

• Basic models require manual cleaning
• May clog if not maintained regularly

Ideal for: Ponds with medium fish loads, and owners who want discreet, convenient, and flexible units.

Koi Pond Filters: Heavy Duty and Powerful

Koi carp product a lot of waste, and are required to be kept in larger, deeper ponds. Standard box or pressure filters are often unsuitable for these ponds. Most keepers tend to favour gravity-fed filters, which feature bottom drains as well as skimmers to pull waste from the water surface and pond floor into large filters. Water is then directed through mechanical and biological media, treated with UV, and then pumped back into your pond. These filter systems often use settlement chambers, sieves, or drum filters to remove solid waste, which is then easily flushed out. 

Pros:

• Handles high loads of waste
• Designed for larger ponds and high-flow systems
• Supports excellent water quality and fish health
• Purpose-built

Cons:

• Requires planning in advance, and is better to incorporate during construction

Ideal for: Large Koi ponds

All-In-One Filters: Compact and convenient

For small ponds, you can keep things simple with an all-in-one unit. These filters combine a pump, filter, and UV into one submersible, compact unit. With an easy plug and play set up, you can have it up and running in as long as it takes to place in your pond and plug in. Some units even come with fountain attachments, or connections for a small stream.

Pros:

• Simple and straightforward
• Perfect for beginners
• Compact and cost-effective

Cons:

• Requires removal from the pond for regular maintenance
• Not suitable for large fish loads or Koi ponds

Ideal for: Small ponds under 2000-3000 litres, with low stocking.

UV Clarifiers: Rid your pond of green water

A clarifier is an important part of any pond filtration system, if you want to prevent floating algae from causing green water. As water flows through the UV unit, the light kills microscopic floating algae before it can spread. Some filters include a built-in clarifier, but the basic models may require a separate UV to be installed between the pump and the filter.

As you cannot over-filter a pond, larger filters mean better water clarity, as well as healthier fish. Over-filtering is even recommended for ponds that are well-stocked, so we always recommend purchasing the largest filter possible.

Finding your perfect filtration system

At Swell UK, we know every pond has different needs, and the right filtration makes all the difference. Whether you're keeping goldfish in a small pond, or managing a large, well-stocked set up, there's a system that has been built to suit your needs.

From compact units for discretion, to large, powerful models, our range covers every type of pond and budget. Add a UV unit and you'll be well on your way to crystal clear water, and a healthy environment to support aquatic life. 

Ready to upgrade your pond?

Explore our selection of filters, pumps, and UVs today. From top brands at low prices, you can find the perfect system to keep your pond clear and thriving. With years of hands-on experience, our pond experts help pond keepers find the perfect setup, no matter the pond type you're building.