What type of pond filter do I need?

“What pond filter….” is the start of one of our favourite questions. #

Here at Shirley Aquatics we’ve been experts in pond filters and pond filtration since 1939. We’re here to help you establish which pond filter you need, and why you need it.

We pride ourselves on our wide range of pond filters and koi filtration products as well as years of practical experience & advice across our team.

We stock an extensive selection of pond pumps from some of the world’s best manufactures such as Oase, Hozelock, Bermuda, laguna and Evolution aqua. We also carry many different types of pond filters. These include pressurised pond filters, nexus units, easypods, self-cleaning filters, low maintenance pond filters, all in one pond pump and filters, the list goes on and on!

Most pond filters will also come fitted with a UV sterilizer. Don’t worry if yours doesn’t we’ll be able to provide one separately should you need one. If you can’t find the pond filter you are looking for the please contact us as we will do our very best to source it for you.

Which pond filter best suits my needs? #

Over the years we have tried and tested hundreds of different pond filters and refined our product range to suit the needs of every pond keeper. Whether you are after a simple in-pond filter or a revolutionary easy to clean koi pond filter, we’ve got the pond filter for you!

We often find customers want to purchase their filter in person so as to ask as many questions they need to about wh pond filter they may need. We love talking about your pond setup but if you can’t get to our store for any reason we hope this brief article will help you make your decision.

Is a pond filter really necessary?             #

You don’t get pond filters in nature and yet we have some beautiful lakes around us stocked up with lots of fish and plants, so is a pond filter really necessary?

Often in natural bodies of water you have a natural source of running water, with either a stream or spring flowing into the lake. This provides a natural source of running water that adds oxygen and also helps to flush away nutrients or fish waste. In bodies of water that do not have this such as man-made lakes, a natural balance has been created between the levels of fish in the lake producing waste and an incredible wealth of plants and bacteria that help to remove the waste and maintain a balance. Where this balance has not been achieved you often see algae problems, as the algae acts as a filter sucking up the excessive nutrients.

You may choose to recreate this natural environment without using a pond filter. To do this you would need to introduce a wide variety of pond plants to act as a natural filter and this balance may take a number of years to achieve, especially on a small pond. The reason for this is down to the volume of the water itself. In smaller volumes of water any changes to the water chemistry cannot be ‘buffered’ or ‘diluted’ as well – meaning changes, and consequences, happen fast.

In most cases, the quantity of fish required and the number of plants installed does not lead to clear water.

A pond filter cannot run on its own. It needs a pond pump to supply it with water, the pond filter then acts as a sewage treatment plant, removing waste from the water and also in the case of a UV clearing the water as well

Fitting a pond pump and pond filter will ensure you provide your fish with the best quality of water to live in.

Do I really need a filter with an ultraviolet sterilizer?             #

The job of any pond filter is to make the water inhabitable for fish and other animals. This means getting rid of a lot of dissolved waste. A filter will give you healthy water but will not necessarily give you clear water. Green water is caused by single celled algae. These are often too fine and pass straight though any filter. The job of an ultraviolet sterilizer (UV) is to kill the algae. The remnants of the algae then clump together and are easily taken out by your filter.

You can have a filter without a UV but don’t expect to have clear water. However you must not use a UV without a filter as the dead algae will have nowhere to go and will just rot in your pond creating more problems.

What should you consider when buying a filter? #

The biggest consideration when selecting a pond filter should be;

Is this pond filter big enough to do the job? #

Most manufacturers will give you guidance as to the maximum size pond their pond filter will look after. In our experience the best way to interpret this is to say in “ideal conditions” this filter will look after a pond of ‘X’ size. The performance of the filter can be affected by the amount of sunlight you get each day, the shape of your pond, the size of your pump, the number of plants you have as well as the size, quantity and variety of fish you have. Not to mention the amount and type of food you feed!

There are so many variables that you cannot begin to take into consideration when buying a pond filter. We have found a safe way around this. Firstly, half the maximum filter capacity to give you a figure for the average pond. If you intend to keep koi or the pond is in full sunlight then half this again. For example, The OASE Biosmart 20000 says it will filter up to 20,000 litres. We would always recommend halving this, so it would be suitable for an average garden pond up to 10,000 litres. But if koi are involved or direct sunlight for a lot of the day then the filter will only cope with a pond of 5,000 litres.

OASE are one of the manufacturers who have cottoned on to this over the past few years and actually state as much on their box. This is a useful calculation to use for any filter unless it specifically states this filter will cope with a koi pond up to ‘X’ size. As you can then be sure that the manufacturers have tested their filter with the messiest fish around!

Is it low maintenance? #

A pond filter might seem like a bargain, but how easy is it to clean, how regularly will you need to clean it and how often do you need to change the filter media? These are all very important considerations when buying a pond filter as you want to spend more time enjoying your pond and less time looking after it!

If you’d like to see a video on what happens if you don’t clean your filter (and let’s face it, who wouldn’t) follow this link. 

Is it going to cost a lot to run? #

In nearly all cases the only electrical part of a pond filter is the UV and these at most will be 55w so a pond filter is one of the cheapest components of your pond system to run

What types of filter are available? #

There are many different types of pond filters, and once you have established the size you need it’s all down to where you want to put it and how much maintenance you want to do. Unless you go to the highest level of pond filtration, a self-cleaning pond filter is not available. Therefore, it is wise to choose the one that is easiest to clean.

Also consider how much the replacement filter elements are and how long each pond filter maintenance is going to take you. Pond filters can be divided into in pond filters, pressure filters, gravity feed filters and gravity return filters.

In Pond Filters #

These are becoming very popular as you have one piece of equipment sitting in the pond which pumps water, filters the water and has a UV to kill Algae. They have one mains cable and are often very economical to run. The down side is that they are really only for smaller ponds and that you have to take the unit out of the pond to clean it. But on the whole, as long as you choose the correct one for your size of pond the work very well and are probably one of the most convenient ways of supplying a pump and filter for your small pond or feature.

Pressurised filters #

These are probably the most popular form of pond filter today. Manufacturers such as Oase, Hozelock, laguna and Bermuda all have at least one range of pressure filters. In some cases these manufacturers have an economy version and a “bells and whistles” version with an easy cleaning facility such as the Oase Filtoclear. Most manufacturers will also do a pump and filter package like the Hozelock Easyclear sets. These make sure you get the right sized pond pump with your pond filter.

Pressure filters are made up of a cylinder that contains the filter media and a lid that seals tightly onto the cylinder that houses the UV sterilizer. Water is delivered to the filter from your pond pump under pressure, passes through the media and leaves under pressure. This means it does not matter where you place it, as long as it is outside the pond it can be below water level or right up in the air. Water can then pass from your pressurized filter up to a water fall or feature. In this respect they are perfect for raised ponds.

The down side to these filters is they often have a limited amount of media in them due to their smaller size and unless you choose one with a cleaning mechanism you have to open them up each time you want to maintain the filter. They are not ideally suited for a koi pond as they rely almost exclusively on foams and koi being messy fish the amount of maintenance required can get out of hand.

Gravity return filters #

Gravity return pond filters are the traditional box filter that most people are familiar with. They consist of a plastic tank with foams and plastic media in. water enters at the top under pressure from your pond pump and then leaves at the bottom via gravity. The outlet of these filters MUST be above the water level in your pond for the water to fall out of the filter and back to your pond. They are often situated at the top of waterfalls or by the side of the pond.

Their lack of positioning flexibility in comparison to pressurised pond filters has led to them taking a bit of a back seat in recent years, although they are often cheaper and work just as well. Pump and filter packages are also available and some of the manufacturers have made these filters even easier to clean as is the case of the OASE Biosmart systems

Multi-purpose koi filters #

There have been a number of filters emerge recently with koi in mind. That is not to say they are not for the average pond keeper just that in most cases people like the idea of having koi in their garden pond but don’t want the hassle of all the maintenance.

The Easypod or Nexus systems are ideal for koi ponds or general garden ponds. They maximise the filtration whilst minimising maintenance. All of these filters can be installed easily, require no replacement filtration elements and have the simplest level of maintenance that you can do with a beer or a cup of tea in your hand! They are the filter everyone should have!