Make a Hydroponic Bog Garden
by Jasmin Malik Chua, Jersey City, USA on 08.24.07
The grand-prize winner of the TreeHugger/Popular Science/Instructables Go Green! contest presented an innovative solution to the evergreen problem of conserving water: A hydroponic bog garden that recycles the water from a sewage tank and produces a water effluent clean enough to discharge into surrounded ponds, ditches, and waterways—or even for irrigation.
An essential component of the bog is alfagrog, a highly porous volcanic rock with plenty of surface area, that houses colonies of bacteria that are responsible for filtering and cleaning any water that passes through. (Koi keepers love this rock because it keeps their fish happy, which means that they're happy. You wouldn't expect all that happiness to come from a humble rock but you see, it happens.)
Because the bacteria in question are aerobic in nature, meaning that they need oxygenated conditions to survive, our bog makers had to add a compressor and rubber aerator to dissolve oxygen into the water coming from the nearby sewage tank. Add several herbaceous, moisture-loving plants, and voila, you have a bio-filtration system you can even fill up with wriggly, happy fish.
Okay, so it's slightly more involved than that, but we'll defer to the experts for the details. Step-by-step instructions, complete with pictures can be found at Instructables.com. Congratulations, Biotank! ::Instructables
Volcanic rock is almost never used in koi keeping anymore. There are other, better, much more efficient methods of biological filtration. Something like an air-fluidized bed with kaldnes biological filtration media, or a trickle tower with ceramic porous media is going to work FAR better than a bog full of lava rock.
It's a neat idea, but see how well it works a couple of years down the road when the volcanic rock gets all nasty, clogged, and fouled up, and it WILL happen. That's when things get all anaerobic and the stink really starts to fly.
They don't use volcanic rock in sewage treatment plants for good reason - it doesn't retain its effectiveness. Most koi keepers have learned from the sewage treatment guys and employ basically the same methods to filter their ponds.
As another aside, a serious koi keeper would NEVER keep rock in the actual pond - any rock belongs in the filter or around the outside as decoration. Rocks in the pond encourage the aforementioned anaerobic bacteria, which can cause all kinda problems with fish health. It also makes it a massive chore to clean the pond, whereas a well designed pond can be cleaned with a simple ten minutes of flushing the filter tanks every once in a while.
It's too bad that Koi never lived in natural ecosystems with self-regulating feedbacks that kept their original ponds clean. Because if they did we could emulate those ecosystems and have ponds without loads of gadgetry.