Pressurised pond filters.

Pressure filters for garden ponds first appeared on retailers’ shelves just over 10 years ago. Most of us were then more familiar with the aquarium pressurised canister filters. These top-end pieces of aquarium hardware  worked perfectly, undisturbed for months hidden inside the aquarium cabinet . Many of us still associate these filters with the musty flavour of aquarium water you would soon taste if you didn’t get the timing of the siphon just right!

Then some bright spark must have thought ‘hey – let’s adapt this principle of filtration for ponds’. This concept initially didn’t seem to make sense. But we soon realised that just as an aquarium canister filter had to be situated below the water level for it to work, this same feature would prove to offer a real benefit for pondkeepers keen on maintaining the natural aesthetics of their back garden. – At last, a filter that could be hidden completely from view, buried under ground.

But let’s be honest – hands up if you were one of the many who had their doubts. After all, how could something that would filter a small aquarium adequately, be expected to achieve the same results in a garden pond containing hundreds of gallons of water – as well as its fair share of blanket weed?

Well 10 years later, and many improved models (and new entrants) later, the pond pressure filter market has certainly become established in our industry as a very popular means of pond filtration. Manufacturers have been keen to add their versions of pressure filter to the wholesalers’ listings in a bid to claim their percentage of a growing market. At the same time, this competitive thrust of new product launches has meant that quality, effectiveness and value have all been improvements that result from this period of competition-led innovation. So after the initial scepticism – how has the pressure filter become so popular?

Where were we before?

The black box filter. The staple filter for an average (500 gallon) pond in the mid 1990’s was a black box filter. This consisted of a rectangular black header tank (the sort that would be more at home in a loft) or similar, filled with filter media. They worked, and still work very well to this day – in fact this style of filter still accounts for a significant part of the market. They were easy to install and met the price-points demanded by the average pond keeper. But they had one major flaw – their appearance. The black box filter had been developed from a product perspective – that is, something that did its job – and little more. I remember when I worked in aquatic retail, to overcome a customer’s resistance against their non-ornamental appearance, we would stock mini-conifers and large pieces of rock so that customers could hide the filter, allowing their pond to look less contrived. Black box filters are pump-fed which means that once the pumped water enters the filter, it flows through the media via gravity, returning to the pond (often via a waterfall) under gravity also. So for a black box to work, it had to be placed above the pond, and above the waterfall which was often the garden’s highest point – quite an eye-sore, and almost impossible to hide.

Pressurised Filters – The filters you can bury.

The pressurised filter’s main selling point (and means of entry into the market) is that it is a filter that is sympathetic to the natural looks a pond keeper tries to create in their back garden. That is, one where the fish, plants and water take centre stage – with no visual clues given as to  how the pond is sustained. Basically, any visible black plastic spoils the illusion – and the pressurised filter has no black on show at all – it’s buried out of sight.

Why can they be buried?

Pressurised filters get their name because they are completely sealed units. The water pressure created by the pump in the pond is carried through the filter, returning the filtered water under pressure. Thus, these filters can not only be buried, but sited below a water fall and still supply it with a good flow of water.

It is accepted that pressurised filters do not have the filtration capacity as a typical black box filter and can be biologically and most definitely mechanically challenged. This means that maintenance and back washing are required more frequently with a pressurised filter.

But it is also fair to say that through changes in design, choice of media and overall volume of pressure filters, some maintenance issues have been addressed, allowing longer between cleans. Most units incorporate a pressure indicator which shows when the pressure is building such that the media needs to be cleaned. Further recent innovations in backwashing and other self-cleaning designs have also addressed the inevitable maintenance issues realised by this type of unit – making them even more user-friendly.

To remain a credible alternative to the very effective black box type filter, pressurised filters had to offer similar performance in other areas. By the mid 1990’s it was common for most black box filters to incorporate a UVc to create a crystal clear pond as standard. Later models of pressurised filter started to incorporate an integral (and in true pressure filter-style – hidden) UVc to provide the same algae-busting feature.

Made to measure.

Despite the endeavours by manufacturers to make pressure filters easier to clean, they are still best targeted at smaller ponds. The majority of new ponds that are installed every year are 750 gallons or less – and therefore perfect for the inconspicuous pressurised filter. However, except for a few larger available units, ponds over 1000 gallons that are stocked accordingly can prove too much of a challenge for a pressurised filter, making open-type trickle filters the best option (i.e. back to the black box-type option).

From the filter stockists’ perspective, the relative small size of pressurised filters also means that they take up less stock room or shelf-space – giving your store potentially more profit per square foot.

Installing a pressurised filter.

Another major benefit to the pond keeper who chooses a pressure filter (and the retailer who advises them) is how straight forward they are to install. All the customer will need is a pump, the filter and two lengths of hose. Ensure that the pump will turnover the pond’s volume every 2 hours (minimum) and that the pressurised filter is rated at the pond’s volume. I like to recommend opting for an overcapacity on filtration and pump output as this will mean there will be less frequent filter maintenance for your customer. It’s not possible to over filter a pond.

In summary, pressurised filters offer both the retailer and pond keeper many opportunities. For the pondkeeper, a filter that is both easy to install and conceal and for the retailer, a filter that will fit in-store on the shelf, and meet the aesthetic demands of their customer.

Models on the market.

Oase – Filtoclear range – several different sizes for ponds up to 15,000 litres

Fishmate Pressurised Pond Filters – several different sizes for ponds up to 15,000 litres

Hozelock Cyprio Bioforce – several different sizes for ponds up to 9000 litres.


1. A typical black-box type filter. (green in this case) – Very effective but difficult to hide.

2. The pressure filter. Easy to conceal by burying. Note the third outlet – this takes dirty filter water ‘to waste’ when the filter is backwashed.

Kill blanketweed and string algae.