Aquaponic Gardening is the hottest thing since Justin Bieber. And for my money at least, is a whole lot cooler. Aquaponics is a symbiotic gardening method that uses a recirculating system to grow both fish and plants. The short version goes like this, as the fish breathe and poo, they create solid waste and put ammonia into the water both from their excrement and from gill activity. Ammonia is bad for the fish. The water is pumped out either directly into a grow bed, or through a bio filter of some kind where bacteria converts the ammonia first to Nitrites then to Nitrates. The plants use the nitrates (and other micro nutrients) as food. The water is thus purified and pumped or drained back into the fish tank as fresh water for the fish.
This is simple and mimics nature. It does, though, have a few minor problems that require inputs and therefore impact sustainability.
The pH in the water needs to be monitored and occasionally adjusted. This is easily done by adding some calcium in the form of crushed sea shells or even egg shells. The plants require iron which must be added. A tablespoon of chelated iron every few months does the trick. I have also heard that suspending some old angle iron, rebar or even nails in the water and rubbing them periodically as they rust, will add iron. I have not tried that one.
The recirculating allegedly requires only a fraction of the water normally associated with gardening, which is great for the environment and the budget. It is also this recirculation that creates the sustainability restrictions, and in an emergency situation, could be a fatal flaw. It requires electricity.
First, electricity is required to run the pump or pumps in the system. Secondly, depending on the variety of fish, electricity is needed to keep the water temperature at a suitable level. For example, the most popular fish in American Aquaponics Systems is Tilapia. Tilapia will quickly die if the water temperature drops below 55 degrees F. Also, many plants won’t grow in cold water. And lets not forget that if you’re growing inside, electricity is needed to power the grow lights.
I’m aware that both passive and active solar can provide ways to heat water in the cooler months. I also know it’s possible to use heat generated from wood stoves, if properly vented, but the water must still be transported through the system and that is a problem. Every system I’ve seen, whether floating raft or flood and drain has at least one pump. This is troublesome for those of us who want to be as sustainable as possible.
Currently, most affordable solar pumps will only work during daylight hours, so the water stops circulating during the dark periods. This is fine for the plants, but fish will quickly die if there is not enough oxygen in the water.
I’m not sure what the answer is. For now, we’re just using electricity and compromising my principles, but in the long run I have to find a solution.
Perhaps investing in a bank of batteries and solar panels will help, but that will require an ac/dc inverter. Even then, I don’t know if a system will run all night. It might demand that we run the circulation during the day and use the battery bank to run air stones through the night.
Perhaps there is a way to use a a siphon that runs continuously. My instincts tell me that would work for a barrel ponics or other small system that has a single grow bed, but might not work as well with larger, multiple bed units.
I am not an engineer, so these challenges vex me terribly. I want to know that in the event of an extended electricity outage that we can continue to use fish and plants together to assist in Our Edible Suburb.
A workaround might be to drain 20 or 30 percent of a tank on a daily basis, use the water to water traditional raised beds and replace the tank water with dechlorinated tap water, well water or captured rain water. If the tank is large enough and the stocking density low enough, this might work during warmer weather as long as enough water is turned over daily to prevent ammonia build up in the fish tank or to cause oxygen to be lost. A simple siphon running from the tank up into a bucket filled with filter media that drains directly into the fish tank, might just eliminate both of those problems.
As you can see, I have more questions than answers. Aquaponic Gardening may very well be the chosen garden method of the future. It has incredible potential. It has, though, a few steps to go, before it is truly sustainable. Until then, we make compromises and try to become creative in our inventions. Or, at the very least, to steal ideas form other people. So, if you have any ideas I can steal, please feel free to share them…