Are you thinking of buying pressure filter for your garden pond but would like to know how they work before you purchase one, then read on.
A pressure filter is a simple set up that’s circular in shape and filled with filter media.
On the top of the filter you will find three inlets/outlets, one of them is the inlet were the pond water is pumped into the filter from a submersible pump that sits on the bottom of your pond.
The water enters the filter and passes over a UVC (ultraviolet clarifier), this is an ultraviolet light that kills the single cell algae that causes you pond to turn green, once the algae is killed it clumps together making it large enough to be removed by the mechanical filter.
Some pressure filters don’t have a UVC but the majority of them do but have a quick check to make sure.
Once the pond water has passed the UVC it then goes through a mechanical filter, the mechanical filters job is to remove all the large particles of waste and debris, this is crucial if you want nice clear water in your pond.
After the mechanical filter comes the biological filter, the biological filters job is to turn harmful ammonia in the water to nitrites and then the nitrites to the less toxic nitrates.
The biological filter contains good bacteria, and its that good bacteria that turns the ammonia into nitrates, but it does take 4-6 weeks for that good bacteria to build up sufficiently in number to do their work properly, so take that into account when adding a new filter system into your pond.
As the name implies this filter is run under pressure, so the pressure of the water entering the filter is more or less the same pressure when it leaves.
Having a pressure filter has some very good advantages over gravity fed filters.
They can be retro fitted anywhere, they don’t have to be close to the pond for them to work.
As the water is pumped under pressure from the filter it can be fitted below the surface of the water and the majority of pond owners bury them in the ground near the pond just leaving the top sticking out. You can then use a fake rock to disguise it.
If you don’t want to bury it, they can be left freestanding, great if you want to keep it in a shed out of the way.
The outlet from the filter can be directed to anywhere you want the clean water to flow.
As the filter is under pressure the water can be pushed uphill, great for pumping water up to the top of a waterfall or to the start of a stream. You can have the outlet pipe entering straight into the pond if you don’t want to run water features.
There is one more outlet on top of the filter and this is for self-cleaning, each pressure filter has its own system for how it cleans the filters.
Usually there is a knob to turn which redirects the water flow from flowing through the filters to exiting the cleaning outlet.
You can connect a hose onto the cleaning outlet and depending on which pressure filter you push/pull a handle up and down or turn a handle, each one turns or squashes the mechanical filters which loosens the captured waste and is flushed through the cleaning outlet.
There’s usually an indicator somewhere on the top of the filter that shows when the filter needs cleaning.
Having this easy clean system on a pressure filter means no more getting your hands wet as you would if you had a gravity fed filter where you have to take out the mechanical filters and clean them by hand in a bucket of pond water.
Not all pressure filters have all the filters inside them, you can buy filters that only have mechanical filters which can be used in conjunction with a biological filer system and some come with both mechanical and biological filters but no UVC.
So there you have it, that’s how a pressure filter works in a garden pond, just remember to use the right sized pump and leave it to grow a good colony of good bacteria on the biological filter before introducing fish into your pond.
Check out our review of the best pressure filters for you pond here