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.  Ill 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

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Cleaning New Gravel and Pipe Size

Cleaning Gravel:

Yesterday I cleaned about 5 cubic feet of new gravel.  In the past I have used progressive tubs and a bucket filled with holes.  I would start at one end and work my way down three or four barrels of progressively cleaner water.  This proved to be insufficient and the barrels became quite dirty very quickly which meant that I would constantly have to start over with more clean water.

But yesterday I used a small cement mixer.  Id put 10 shovel fulls of gravel in and filled it with water.  Then turn the mixer on for 15 seconds, and dump the water.  I did do this about 7 or 8 times until the water was running clear.

This next step may not be necessary, but then I did a final rinse in a white bucket.  I was able to easily see how clean the water was in the white bucket, and two quick rinses generally finished the job.

It took a few hours to perform this cleaning, but after several bad experiences with cloudy water, Im very happy with the results.  Today my water is perfectly clear.  

Pipe Size:

A couple months ago I added 10 feet of 1-1/4" pipe to the line from my fish tank to the grow bed.  It has worked well until recently when I noticed that the water in the fish tank was beginning to raise.  Closer inspection of the pipe revealed that gunk had built up on the surface and was slowing the water down.   I replaced the pipe with a clean 2" pipe.   Ill let you know in a few months how that worked out.   Im feeling confident that this is going to work out much better.    As a general rule Id say 2" or larger pipe should be used everywhere.

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