Installing a pond filter: the pump, UV and filter order and the right connections
Most filtration problems come down to a poorly planned installation: the pump in the wrong place, a hose that is too narrow, the UV in the wrong spot. The order of the components and the type of filter make all the difference. Here is how to set up a pond filter correctly.
The order to remember
- Pump at the deepest point, opposite the water return.
- UV lamp just before the filter (often built into the filter).
- Filter: mechanical, then biological.
- Return to the pond via a waterfall, a stream or a hose.
Why the UV before the filter?
The UV lamp makes suspended algae clump together. Placed before the filter, it allows the filter to trap these clumps in its foams. Placed after it, the clumps go back into the pond and feed it.
Pressure filter: the simplest option
The pump pushes the water through the filter, which is closed and watertight. The filter can therefore be placed higher or lower than the water level, and can even be half buried to keep it out of sight. The water can then rise up to a waterfall.
- Ideal for ponds up to about 15 to 20 m³.
- Keep the lid and the cleaning lever accessible.
FiltoClear Set 16000 - Complete pressure filter kit - Oase
Pressure filter with built-in UV, pump and hose, ready to install. Live price and instant add to cart:
Gravity filter: bigger, more efficient
The filter is open and the water flows out of it by gravity. It must therefore be placed higher than the pond surface, and the return pipe must slope down continuously, with no high point. A gravity filter placed too low or with a return pipe that is too narrow will overflow.
- The pump flow rate must not exceed what the filter can handle.
- The return pipe must be wider than the inlet hose.
- Stand the filter on stable, perfectly level ground.
BioTec ScreenMatic² 40000 - Gravity filter - Oase
Gravity filter with simplified cleaning for larger or well-stocked ponds. Live price and instant add to cart:
Hoses and fittings
- Spiral-reinforced hose: it does not kink or collapse, even when buried or bent.
- The right diameter: a hose that is too narrow can sharply reduce the actual flow rate. Use at least the diameter of the pump outlet.
- The shortest route with as few bends as possible.
- Stainless steel hose clips on every connection.
Flexible PVC hose 32 mm, spiral-reinforced
Spiral hose to connect pump, UV and filter without losing flow. Live price and instant add to cart:
Read also
For the connections, read The benefits of using flexible fittings for your pond and filter.
READ THE ARTICLEThe pump
Place it at the deepest point, slightly raised so it does not suck up sludge, and opposite the water return so that the whole pond circulates. It should pass the entire volume through in 1 to 2 hours, taking into account the head height and the length of hose.
AquaMax Eco Classic 8500 - Pond pump - Oase
Energy-saving filter pump that copes with debris-laden water. Live price and instant add to cart:
Read also
For a small pond, see Which filtration system should you choose for a 500-litre pond?.
READ THE ARTICLETo get everything in one go, discover our complete filtration kits.
Comparing the two set-ups
The order of the components stays the same, but the way the water returns changes everything. A pressure filter receives the water pushed by the pump, whereas a gravity filter lets it flow back under its own weight. The diagram below helps you see where to place each component.
Working out the flow rate you need
The rule mentioned above, passing the entire volume through in 1 to 2 hours, is easy to apply. Example for a 6 m³ pond: you need an actual flow rate of about 3,000 to 6,000 l/h. This must be the flow that actually reaches the filter, not the figure printed large on the box, which is a maximum with no head height and no hose.
Check the flow curve in the instructions at the real head height to be overcome, and add a margin if the route is long. Also make sure the chosen flow rate is compatible with the UV-C lamp and with the filter. If in doubt, our guide to choosing a pond filter goes through the criteria to look at before volume.
Commissioning, step by step
- Dry-fit all the components to check the hose lengths and access to the lids.
- Tighten every connection with a clip, then check the position of the filter with a spirit level.
- Fill the gravity filter if the instructions require it, then start the pump without the UV-C lamp.
- Watch all the joints for fifteen minutes: not a single drop should appear.
- Switch on the UV-C once the circuit is full of water and stable.
- Check again the next day, then the following week: a connection can loosen and a filter can settle.
On the electrical side, plan a sheltered spot for the connections, and never pull a pump by its cable. Our article how to connect a pond pump covers the safety points and common mistakes.
Stainless steel hose clip304 stainless steel, worm-drive tightening, several diameters.View productOase Bitron C 24 WUV-C unit to fit before the filter, according to pond volume.View product
Always leave free access around the filter, even if it is hidden by plants. A filter that is hard to open ends up being cleaned too late. Also think about where the dirty rinse water will drain: a nearby flower bed is more practical than a patio.
Frequently asked questions
Why is my filter overflowing?
On a gravity filter: pump flow too high, clogged foams, or a return pipe that is too narrow or not sloped enough. On a pressure filter: lid or seal not closed properly.
Should the filter run at night?
Yes, 24 hours a day during the season. The bacteria in the filter need a constant flow of water.
Do I need a residual current device (RCD)?
Yes. Every electrical pond appliance must be plugged into an outdoor socket protected by a 30 mA RCD.
In summary
- Pump, UV, filter, return: in that order.
- Pressure filter: at any height.
- Gravity filter: above the water level, sloping return.
- Spiral hose of the right diameter, short route.
Sources and references
- Oase pond filter installation instructions
- Hands-on experience from Aquiflor, aquatic garden centre in Nodebais (Belgium) for over 30 years
- Questions received by the Foudebassin.com customer service team
Last updated: 28 September 2026.
Leave a comment