I built this aquaponics system a year ago to grow fresh leafy veggies for the household. It consists of a 700 litre fibreglass pond inhabited by koi with two 50 litre gravel filled grow beds suspended above. If you've never encountered aquaponics before, it's a combination of aquaculture (fish keeping) and hydroponics (growing plants without soil). The water from the fish tank is pumped into the grow beds where the plants consume the nutrients. This removes waste from the water, cleaning it for the fish.
The image above shows three to four weeks growth from seedlings. I harvest from it consistently and the growth rate tends to keep up the supply. There's plenty of veggies in there including varieties of spinach, lettuce and kale. A 1600 ltr/hr pump runs continuously moving the water through a length of 19mm poly pipe which is routed to each grow bed through adjustable valves.
This is a flood-and-drain setup where the grow beds are filled with water then drained by a bell siphon repeatedly. A bell siphon empties the grow bed once the water level reaches a set height by creating a siphon that ejects the water far quicker than the pump can fill the bed. Once emptied, the siphon will break and it will begin filling again. See the notes at the bottom for an explanation of the construction and theory of auto siphons as it's too long for this short post. This continuous cycle allows the plant roots to consume nutrients from the water when it's full and oxygen when drained.
I cobbled this stand together so the fibreglass pond wasn't bearing the weight of the grow beds. It took some effort to get it all together but once setup there's very little maintenance. Most of time you just need to feed the fish each morning. There's no filter on the pump as the solid fish waste is benefitial to the grow beds. This causes the pipework to clog a bit quicker than usual but it's remedied by a good blast from the hose. Every couple of months I add a capful of seaweed extract to fertilize and make sure to keep the system topped up as water is lost through plant growth and evaporation.
After six months of operation, I added some worms to the beds although I was skeptical how well they would fare. After clearing the beds recently to re-plant, I found they had multiplied in number and were doing just fine. Growth rates improve over time as the system matures. If you have any questions, feel free to leave a comment.
- Bell siphon explained - http://www.ctahr.hawaii.edu/oc/freepubs/pdf/BIO-10.pdf