Filtreau Combi-AFTER Drum Filter with UVC – Gravity Fed

Filtreau Combi-AFTER Drum Filter with UVC – Gravity Fed

A narrow-format combi for a gravity-fed filter bay

The Combi-AFTER Gravity is a long, narrow drum-and-biological filter for installations where a broader combi will not fit comfortably. Its body is 1,730 mm long and 570 mm wide, giving a different layout from the shorter, wider Combi-NEXT.

Included media: this package comes with approximately 100 litres of moving-bed media. Allow for this included quantity before ordering any extra media; an appropriately sized external air pump is still required.

This is a combi filter with its own mechanical drum stage, not simply a polishing chamber that must sit after another drum. The gravity-fed version receives pond water before the circulation pump, with the operating level set to suit the pond.

Mechanical separation and biological treatment

The 120-micron screen removes suspended solids. Loading changes the water level and starts an automatic rinse, rotating the drum so the spray bar can wash debris into the waste channel. Removing waste first helps keep the biological section cleaner.

The moving-bed area supports biological media that treats dissolved fish waste once mature. A fitted 40W amalgam UV-C unit helps control suspended algae. The drum, media and UV work on different problems, so a clear-looking pond still needs proper biological capacity and water testing.

This version uses a separate cleaning-water arrangement

There is no internal rinse pump in the FS421 package. Specify a compatible external pressure-water supply as part of the installation. If a mains-fed arrangement is chosen, its controls and backflow protection must be suitable; an unprotected direct connection is not appropriate.

For the same gravity-fed AFTER layout with the pressure-cleaning pump built in, see the Combi-AFTER with rinse pump. The cleaning pump is separate from the circulation pump that moves water around the pond.

Media, aeration and service space

Choose the media loading around the actual chamber and retention fittings, allowing for any media included in your selected offer. Leave enough free water for the moving media to circulate rather than packing the chamber solid. The fitted diffuser needs a separate air pump chosen for output at operating depth.

Do not add Japanese matting to the moving-media section as though it were a fixed-media cartridge bay. A separate static stage can be designed where required. Increase feeding gradually while media matures and use ammonia and nitrite results to guide changes.

A narrow body still needs correct plumbing

The maximum flow is 30,000 litres/hour, with three 110 mm inlets and three outlets. Keep drain and skimmer branches accessible for isolation, and avoid squeezing pipes around the body so tightly that routine servicing becomes difficult.

Compare the Combi-NEXT Gravity if a shorter body would suit the filter area better. If your pond pump supplies the dirty inlet above pond level, the relevant alternative is the pump-fed AFTER.

Technical specification

Installation and regular checks

Support the full base and set it at the correct operating water level. Leave clearance above the lid and a clear route for UV lamp and quartz removal. Keep the waste outlet accessible, inspect the screen and nozzles and isolate power before working inside the filter.

Related equipment and advice

• Charles Austen ET100 Airpump
• View the full Filtreau range
• Browse Filtreau drum filters
• Read our drum filter guide
• Compare all drum filters
• Choose a variable pond pump
• Choose a Charles Austen air pump
• Pressure pipe, valves and fittings
• View Filtreau UV-C units
• Find replacement UV lamps and quartz sleeves