This is the more complex type and is suitable for large as well as small ponds.
The unit is housed outside the pond, usually hidden by shrubs at a location close to the top of the waterfall. A surface or submersible pump is used to push or draw water through the inlet pipe. Was is then aerated through jets or holes in a spray bar and passes through one or more layers of filter media.
Several types of media are available (rough surfaced gravel, open cell foam, resin bonded fiber matting, and coarse sand). The clarified and purified water is returned to the pond through the outlet pipe.
