Pond pressure biofilters make good sense in confined spaces. Pressurized pond filters are very efficient especially if they contain Alfagrog

Last week we did the annual exhibition of our fibreglass water features at the UK's premier garden trade show called GLEE. The show is massive and held every year at the National Exhibition Centre in Birmingham.

I have been going to this show for 11 years and always try to "discover" what's "Top Of The Pops" ..... by this I mean not what is new and revolutionary but what has been adopted by the industry in general and has become something of a standard offering. This is a sure sign of success in the marketplace.

This year the product that everyone was offering was the pressurized biofilter and UV combined.

The first company to offer this type of filter was Hozelock Cyprio around 5 years ago.

Most pressurized biofilters are basically cylindrical in shape with inlet and outlet pipes close to the tight fitting lid.

As such a pressure filter is essentially a container that can be operated under pressure and inside which is a mechanical filter system and an UV lamp. The mechanical filter system is normally open celled foam which doubles as a filtration biomedia.

The better models also include additional biomedia like Alfagrog.

The single biggest advantage of a pressurized biofilter is that it can be buried and placed anywhere in the pump circuit (even below the pond level) making hiding much easier than with a box type biofilter.

The first thing you will notice about any pressure biofilter is that it is very compact and immediately begs the question why can a pressure filter be so small yet do the same job as a CONSIDERABLY larger conventional biofilter. Those readers who have been with us for some time will probably know the answer. For the newcomers let me explain ....

The effectiveness of any biofilter has nothing to do with the size of the container. It has much to do with the type of biomedia used and also the effective turbulence produced around the biomedia in the filter itself. You should read my coffee and sugar example to better understand this idea. The higher the turbulence the better is the dissolved oxygen and nitrogen food component placed in the immediate vicinity of the filter bacteria. In this way biofiltration efficiency is increased by an enormous amount.

This means the size of a container can be reduced.

A most important reason allowing the success of the pressure biofilter is the inclusion of an UV lamp which kills water-borne suspended algae. This flocculated algae is then removed in the mechanical filtration section of the pressurized biofilter. If there was no UV lamp then the sponges making up the mechanical filter would block very quickly and create excessive cleaning situations. Bear in mind that most cloudy ponds result from suspended algae and not dirt.

A pressurized biofilter cannot work effectively using a normal pond pump which contains a suction strainer sponge. It is preferable to run a solids handling pump directly through the pressure filter. When flow coming out of the filter falls off it
is time to clean the sponges.

In the best models this can be easily and quickly achieved without opening the filter itself .... avoid any unit which requires opening to clean it. The pressure required to drive water through this type of biofilter is higher than required for a normal box type biofilter and this must be taken into account when selecting a suitable pump.

Special situations requiring extra attention

The capacity of a pressure biofilter when related to any pond is also a function of the fish mass inside the pond and not just the volume. The reason is that more fish produce more waste which means the filter will block up faster. In addition the larger the amount of fish mass then the larger must the pump be to keep the efficiency of bacterial nitrification at a high level. Remember as flow drops then operating efficiency also drops. This is an excellent reason for choosing a pressure filter with Alfagrog inside it. This allows high conversion efficiency to be maintained as the flow drops due to sponges blocking.

What this means in practice is that you must be very careful in selecting the right pressure biofilter and pump. If a unit is described as handling a pond of say 1,000 gallons this would only be the case if there were no fish (ie plants only) in the pond. If the same pond had goldfish then the capacity might drop to say 500 gallons and with koi it could drop to 250 gallons ..... see what I mean?

In summary
1. Choose a pressure biofilter with extra biomedia inside it (not just foam)
2. Choose the size bearing in mind the stated capacity is normally for pond with plants only so read the instructions carefully
3. Choose a suitable (higher pressure, no sponge) pump
4. Choose a pressure biofilter with easy cleaning mechanism.