Gravel Bio Filter

Here is a concept drawing of a bio filter which filters from the bottom up
I have used this is the type of filter for many years without problems.

A spray nozzle is angled on the bottom of the power wash tube which is connected to a garden hose to stir up the waste.
The 2" inlet also serves as a waste drain.
A tee with either a diverter valve or two separate valves allows switching from normal operating to backwash mode.

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This page continues to get a lot of Google hits, so I have added this drawing to demonstrate how the bio-filter in my pond was built.

The gravel media is suspended above an open space.  I did this by building a cement block cistern on top of a 6" concrete slab.  The blocks were laid dry and then filled with concrete.  Inside I laid 1-1/2"x8"x16" paver bricks on edge to create a shelf for the PVC tubes to rest on.

The PVC tubes are 1" pipe and contain a piece of 5/8" rebar to give them the strength to support the gravel.  The ends are capped to prevent the rebar from rusting. Yes it takes a lot of these pipes laid side by side. Over the top of these PVC tubes I placed a piece of PVC fencing material to further support the gravel.

There is a drain and an inlet pipe placed at the bottom.  Both are mortared in place as is the outlet near the top.  Then to prevent leaks I coated the entire inside surface with Thoroseal .

I have also built small filters inside of plastic olive barrels as depicted in the drawing at the top of this page.  The gravel is supported by a PVC cage.  I'll let you use your imagination rather than attempt to draw that.

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 Another idea I have is to plumb the spill tube down to the bottom and bring the inlet to the top.  Dirty water is filtered down through the gravel.  A mesh on top of the gravel would facilitate cleaning

This would facilitate cleaning.  A mesh could be laid on top of the gravel and periodically rinsed off

SketchUp Link