
Photo of the tree removal
The filtration of our pound water is done by the combined effort of the pond plants absorbing the available nutrients and the circulation of water carried out by an aquarium air bubble pump that consumes very little power while displacing large amounts of water. Since the water is moved in a very gentle way - as opposed to conventional pool pumps -, the pond filtration is 100% wildlife friendly. It's also affordable and safe - no electrical cables near the water!
Best of it all, it can be self-built. Take a look below at how it works, it’s much easier to get your head around it once you see all the elements in place.
If you are curious or want to do it yourself, we've used David Pagan-Butler’s tutorial for organic swimming pools as a guideline, which we thoroughly recommend.
How do the pond filtration and rainwater collection work?
We first built a sand bag wall with two holes for soil pipe T junctions at both ends of the wall.

Take a look at both the bottom and top of the photos where you can see the soil pipe T junctions.
The photo below shows another angle, where you can see the sand bag wall height and the black perforated flexible pipes which are attached to the soil pipe T junctions

In this photo, you can also see the white smaller (15mm) pipes which are attached in one end to the aquarium pump (not shown) and in the other end, to air stones placed inside the soil pipe T junction. See below for more photos of how it actually looks like.
The perforated pipes were then filled with gravel. A lot of gravel. The sand bag wall contains the gravel so the pond has a shallow regenerative zone, which is where the plants are and the filtration happens, and a deeper section, where we planted water lilies and where plants called oxygenators found their place without our help. The difference in depth encourages plant and wildlife diversity.

We've used 16 bulky bags of gravel (more than 15 tons) in the whole garden (as a mulch and as a substrate for the pond regeneration zone), all carried by wheelbarrow!!
Here’s how the bubble system looks like.

Photo by David Pagan-Butler

Photo by David Pagan-Butler
The bubbles, which are a lighter mix of air + water, float to the surface through the top opening of the T junction, which draws the water in the perforated pipes across the sandbag wall to the bottom of the T junction, which in turn will transform into bubbles.

Image by David Pagan-Butler
This simple, gentle mechanism is what it takes to put large quantities of pond water in motion. The water inside the perforated pipes will slowly dislocate towards the bottom of T Junction, transforming themselves into bubbles as they come in contact with the air stone. At the same time a new influx of water will pass through the gravel to occupy the 'empty' space in the perforated pipes.
Since it’s a low pressure system, it creates a large amount of water circulation from the gravel to the deeper section of the pond with very little energy consumption.

Image by David Pagan-Butler
Where does the pond water come from?
Our pond is exclusively filled with rainwater. Hidden pipes under the wooden deck carry water from the gutter not only from our house but also the three adjacent houses to ours.
Since we don't top up the pond with tap water the shallow area of the pond will transform into a pebble "beach" in very dry Summers, with the difference that a lot of green will still be seen amongst the gravel.
In wetter weather, a hidden overflow will divert the excess water to the mains sewers, with the advantage that the passage of water will be slowed significantly, preventing water runoff.
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