Pond Filtration: Choosing Your Filter & UV Clarifier

You need a pond filter in order to achieve clean, clear water, and a healthy environment for fish. In this guide we’ll cover how to pick the best unit for your pond based on size, budget, and stocking.

Crystal clear water and healthy fish starts with the right filtration system. With many units available for different pond sizes, stocking levels, and budgets, choosing your system can be daunting. In this guide, we'll explain the options, features, and benefits to help match a system to your pond.

Why your pond needs filtration

A good system removes waste, reduces algae, and helps to maintain healthy water for your fish. Filters work alongside pumps to keep water circulating, while UV clarifiers prevent floating algae, or green water.

Recommendations:

Tip: Always size up where possible, you can't over-filter a pond, but you can under-filter.

Shop our selection of pond filters today for top brands at the best prices.

Types of pond filter

Box Filters: Simple, yet effective

Box filters are one of the most common choices 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 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 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 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 return point, such as the top of a waterfall

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

Shop our range of box filters today.

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 units, water exits a 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.

Browse our selection of pressurised pond filters now.

KKoi Pond Filters: Heavy Duty and Powerful

These fish produce a lot of waste and require larger, more powerful filtration systems. 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 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.cking.

UV Clarifiers: Rid your pond of green water

A clarifier is an important part of any pond 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.

Larger filters mean better water clarity, as well as healthier fish. High filtration levels are even recommended for ponds that are well-stocked, so we always recommend purchasing the largest one possible.

Finding your perfect filtration system

At Swell UK, we know every pond has different needs, and the right system makes all the difference. Whether you're keeping goldfish in a small pond, or managing a large, well-stocked set up, there's a model that has been designed 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. You can easily find the perfect system to keep your pond clear and thriving. With years of hands-on experience, our team of experts help pond keepers find the perfect setup, no matter the pond type you're building.