Garden Pond Filters FAQ

Andy Hobson has put together this FAQ feature on garden pond filters to address some of the questions asked by people new to pond and fish keeping, and hopefully make it easier for others to make their choices.

Created by Andy Hobson (Alumni) on Tuesday, 4th of March, 2014.
Updated on Tuesday, 20th of December, 2016.

A stunning garden pond during spring.

Do I even need a pond filter?

It depends on your pond and what you’re planning to use it for. If you want fish then I would say yes every time, this is because fish create lots of waste and the only real way to get rid of this waste is with a garden pond filter. If left unfiltered, the water can become polluted, poison your fish, cause the water to go cloudy and possibly smell too.

What do the numbers mean on pond filters?

The numbers on filters will normally mean the maximum pond size they are able to filter, however you must be careful with this because these numbers usually mean without fish. Some filters however, like the Hozelock Bioforce Revolution show the pond size they can handle with fish. This is a new idea by Hozelock and it will make things easier for the consumer.

You'll also find that pond filters will list a maximum flow rate, this is the maximum rate of water per hour the filter can handle. You should pay careful attention to this rate when choosing your pump. Too large a pump can overflow a box filter or blow the seals on a pressure filter, too small a pump will mean the filter is unable to efficiently filter the pond.

Which is best, an underwater, pressure or box pond filter?

The type of filter you choose should be based on your pond and not the price, as in the long run you could end up buying a whole new filter system after initially buying the wrong type. I've experienced this scenario with many customers who have commented to me that they wish they had been told the facts in the first place so they didn't make the mistake.

Hozelock EasyClear Underwater Pond FilterUnderwater Pond Filters

These are good for small to medium sized ponds with low fish stocking levels, they’re quick to install and will usually come with a built-in UV clarifier.

The issue with these filters is that for cleaning you need to get them out of the middle of your pond, not something you will want to do when it’s freezing cold outside. They also don’t do well in big ponds or ponds with many fish as they have a very small filter surface area.

Pond Pressure Filters

Hozelock Bioforce Revolution Pond Pressure Filter

These filters are great if you want  to hide the filter but require something a little more substantial than an underwater filter. As they are pressurised they can be located below the water level, for example below and behind a waterfall. 

The issue with pressure filters is that they do need more maintenance than a box filter but not as much as an underwater filter. The more expensive pressure filters tend to have easy-clean options which counter this problem though, which has been a great innovation for the aquatics industry.

Pond Flow-Through Box Filters

Oase Biosmart Flow-Through Box Filter for PondsThese filters are probably seen as old fashioned but you can’t beat them when it comes to the sheer volume of water they’re able to filter and they’re not normally as expensive as the equivalent pressure filter.

The large surface area allows for lots of foams and filter media and a nice big UV clarifier if yours has one, this will keep your pond extremely clean.

The downside is that they’re bigger and obviously harder to hide, especially if you don’t have a huge garden. They are easy to clean though and many of the more expensive box filters come with easy cleaning options. 

A box filter will overflow if the pond pump is too powerful for it so I'd say be extremely careful when checking the maximum flow rate of the box.

Do I need a UV clarifier on my pond filter?

A UV clarifier will eradicate suspended algae, which is informally known as green water. We'd always recommend a UV clarifier because it prevents this unsightly algae. Whether or not to have one really depends on if your pond is well shaded or not, green water is caused by constant sunlight so if it's unshaded I'd definitely say yes.

You will need to change the UV lamp every year, this is because the UV output will diminish over a period of 6-9 months of constant use.

How do I clean my pond filter?

Although there are different ways to clean individual filters, the premise is always the same, never wash your filter out using tap water. Try to use water taken out of the pond if possible, this is because you are not trying to clean the foams and media but rather just unclog them. Using tap water will kill the beneficial bacteria that breaks down the waste.

The easy clean systems built into pond filters will normally use the water from the pond to clean the foams and then the dirty water, which contains useful nutrients, is sent into a flower bed. 

Is bigger always better when it comes to pond filters?

Yes, you can never overfilter your pond water so the larger the filter the better. If you pick a larger filter it will mean less hard work for the filter and less frequent cleaning, meaning less work for yourself too.

Our Pond Filter Range

You can view our full range of pond filters here.

Garden Pond Pumps FAQs.

Related Articles

Bermuda Aquatics Brand Back In Business

Bermuda Aquatics Brand Back In Business

The Bermuda brand is back! That's the great news GardenSite partner Andrew Hall has received from Bob Meacham, National Accounts Manager for the new owners Evolution Aqua.

Author: Martyn Loach

Written by Martyn Loach.
Published on Wednesday, 14th of December, 2016.

November Pond Maintenance

November Pond Maintenance

Aquatic expert Dan Everton has this advice on how to maintain your pond during November, when the days are short, frost threatens and leaves are falling from the trees.

Author: Dan Everton

Written by Dan Everton.
Published on Sunday, 30th of October, 2016.

Tetra Survey Proves Pets Are Good For Children

Tetra Survey Proves Pets Are Good For Children

Tetra have been innovators in the world of aquatics for over 60 years, and Ellie Goodall has been reading a research survey they have recently published proving that keeping a pet is good for your children.

Author: Ellie Goodall

Written by Ellie Goodall.
Published on Monday, 27th of June, 2016.

Reasons To Choose An Intalogs or Blagdon Raised Pond

Reasons To Choose An Intalogs or Blagdon Raised Pond

There's no doubt that building a pre-formed or liner pond involves a certain amount of hard work, so Nathan James Dodd thinks that a raised version from Intalogs or a Blagdon is well worth considering.

Author: Nathan James Dodd

Written by Nathan James Dodd.
Published on Thursday, 12th of May, 2016.

comments powered by Disqus


View RSS Feed


Andy Hobson (Alumni)

former Social Media Co-ordinator

View Profile

Follow Us!

Recent Articles

How to Choose The Right BBQ For Your Needs

How to Choose The Right BBQ For Your Needs

The weather forecast is for a sizzling summer and David Coton is already looking forward to preparing delicious barbecued food for his family and friends. Barbecues have become incredibly popular over recent years and here is David's guide on what to look out for when choosing one of these summer essentials.

Author: David Coton

Written by David Coton.
Published on Friday, 28th of April, 2017.

What Size And Type Of Shed Should I Choose

What Size And Type Of Shed Should I Choose

Sheds of any kind are ubiquitous in the British garden and, due to their popularity, there are plenty to choose from. David Coton explores the basic considerations that need to be taken into account before purchasing one.

Author: David Coton

Written by David Coton.
Published on Friday, 28th of April, 2017.

How To Care For Your Spring Lawn

How To Care For Your Spring Lawn

Pay attention to your lawn in the spring and Andy Taylor reckons you will receive dividends later in the year.

Author: Andrew Taylor

Written by Andrew Taylor.
Published on Wednesday, 9th of March, 2016.

Robert Hall Elected on the GIMA Judging Panel

Robert Hall Elected on the GIMA Judging Panel

Robert Hall, senior partner at has been elected to sit on the Garden Industry Manufacturers Association (GIMA) Judging Panel for 2017. The news was announced on 31st March 2017 on the GIMA website.

Author: David Coton

Written by David Coton.
Published on Friday, 31st of March, 2017.