Aquaponics


Last update: July 30, 2004

Aquaponics is the blending of aquaculture (fish-keeping) and hydroponics (growing plants without soil). In an aquaponic system the fish, plants, and various bacteria form a symbiotic group: the fish eat food and excrete waste. The fish waste is consumed by the bacteria which break it down in to nitrates, which are absorbed by the plants. This cycle helps clean the water of waste products, which keeps the over-all system habitable.

Tabletop system


Established December 6, 2003

Here is an image of a small aquaponic system prototype. This system consists of a 10 gallon capacity aquarium, equipped with a heater and power filter, and a grow bed mounted above the tank. The grow bed is filled with epoxy-coated aquarium gravel (chemically inert), and is fed aquarium water by a small pump salvaged from a table-top foutain. The water is distributed into the grow bed by a tube with multiple perforations buried just below the surface of the gravel. Another perforated tube sits on the bottom of the bed, and is connected to the return tube which drains the water back into the aquarium.

In this system the aquarium is stocked with one plecostomas and three neon tetras. The water temperature is kept between 76 and 78F. A timer runs the aquarium lights for 10 hours per day. The fish are fed flake food once per day, and the pleco also grazes algae that grows on the tank walls. The grow bed was planted with a single cutting from a philodendron houseplant.

The choices of inhabitents for this experimental system were mostly what was available. The aquarium was well established, having run for about three years before the grow bed was added. The plant was a cutting from one growing in a pot in the office. The philodendron is not a bad choice, since it is hardy, doesn't require much light, and cuttings will root in water. In most aquaponic systems the choice of species is made to insure compatibility with each other and their environment. In this specific case, the system is mostly ornamental and is exposed to moderate indoor light levels. A commercial system for producing food fish and crops would obviously require different species, and would be optimized for maximum production rather than asthetics.

Update: Feb 24, 2004
The inital system is working well. The water flow through the grow bed has been somewhat problematic: sometimes the water doesn't flow out quickly enough, and the bed fills to within a couple of inches from the top with water. This happened on and off for a few days when the system was first set up, but then started working properly, keeping only an inch or so of water in the bottom.

When three more plant cuttings were added to the system, the water once again started doing its weird non-flowing bit, but after leaving the pump unplugged overnight, the system worked properly again the next morning. This may be due to a too-small pipe or opening for drainage back into the tank. While changing this would be somewhat of a pain, another possibility being considered is adding a larger overflow pipe higher up on the bed. This would allow water to be routed back to the tank in case the drain line 'plugged' again in a controlled fashion, instead of possibly overflowing the bed container which would make a mess and also possible allow the pump to empty the tank.

In any case, the original plant cutting is quite healthy, although growing more slowly than expected. The two new cuttings were made from the same original plant.

Update: April 4, 2004
The water level in the growbed continues to fluctuate. When the level in the tank gets too low, water is added directly to the bed. The water then flows down the drain into the tank and replenishes the system. For some odd reason, this always seems to cause the water level in the growbed to stay high, even after the pump is unplugged, all the water drains out, and the system is even left this way overnight. I'm speculating that there is either something in the drain tube that gets disturbed and partially plugs the drain holes (maybe a bacterial film), or it could be something as simple as the pump being able to produce more pressure when the tank is full vs. low. In either case, the high level in the growbed causes concern that the water might spill over the edge and onto the carpet. To prevent this, the pump has been left unplugged overnight on several occasions.

Two of the new plant cuttings had their stems die and had to be removed from the system. If this was due to drying out during the pump-off nights, or they just didn't root properly is unknown. The original cutting looks very healthy, and one of the new ones looks ok for the moment.

I plan to switch to a larger diameter drain tube in the near future to try to alleviate the level problem in the growbed.

Update: July 16, 2004
The aquaponic system has been disassembled. The growbed drainage problem never did get solved, and while the original plant flourished, four additional cuttings died. The high water level in the growbed was a continual source of concern, and lowered the water level in the aquarium enough to cause problems with the filter and heater. The whole system also wasn't, well, all that nice-looking. I opted to leave the growbed support platform on the tank and use it for potted plants to improve the appearance of the tank.

This is not the end of my aquaponic experiments, just this first version.

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