In last month's article we discussed the benefits of the Aquaponics method of farming and the components that it is made of. This month we are going to focus on the Aqua in Aquaponics. 

I've been fascinated with soil-less growing techniques since I first visited Epcot almost thirty-years ago. The giant vegetables and dangling roots gave me the inspiration to experiment with my own systems years later and still have a profound effect on my idea of successful gardening today.

Like most hydroponic enthusiasts, I used water soluble macro ingredients to provide my plants with nourishment. My results were often good, but mistakes were costly. Over fertilization or nutrient lock due to PH imbalances caused thriving plants to wilt and stunt. More often than not, I would find myself  "chasing my tail" as I flushed the system or tried to swing the PH back to the desired level, the plants suffering through each ordeal. I continued to look for a more reliable and natural method.

When I discovered the Aquaponics method, I knew that I had found my answer. The efficiency in term of water usage was even better than in a stand-alone Hydroponics system (which is ninety-percent more efficient than typical farming methods). Nutrient burn is non-existent and because of the volume of water and its constant circulation and aeration PH is much easier to maintain. 

The system consists of tanks or ponds for fish, or other aquatic life such as prawn or crayfish; a bioreactor, which converts the fish urine and feces into the full range of macro- and micro- nutrients; and a hydroponics system that, aside from growing plants, filters and cleans the water that is then returned to the tank or pond. Very efficient and sustainable.

Choosing the size of tank or pond is dependent on a number of factors including the space available, the size of the system, and the type of stock being used.  Even a small aquarium can be used to grow an herb garden in your kitchen. A good rule of thumb is that every gallon of reservoir will support two gallons of plant roots and vice-versa two-gallons of plant roots are needed to filter each gallon of reservoir.

Regardless of the size, it's important to be able to keep the reservoir properly oxygenated and at the proper temperature. Oxygen is absorbed by water at the surface, but the amount available quickly diminishes as you go deeper, especially if the water is not being circulated. This can create dead-zones which fish will avoid, effectively diminishing your yield. In smaller applications aquarium air-pumps can be used, however, these are very inefficient and are not scalable to larger systems. A better method for larger systems is to use fountains which circulate the water from the bottom of the reservoir and spray the stream into the air. This also creates surface movement which both improves oxygenation and helps eliminate potential mosquito breeding. Biological debris, such as leaves, host microorganisms that can quickly devour any free oxygen leading to the dreaded dead-zone, so its important to keep your reservoirs free from such accumulation.

Another important consideration is temperature maintenance. The species of stock you choose will determine the optimal temperature for your system. Shallower and smaller systems will tend to fluctuate with the ambient air temperature potentially making it difficult to maintain the ideal. The larger the system, the closer to your areas average temperature will naturally result. This may be a factor when choosing the stock to populate your system.

Your choice of stock will mostly be determined by your location. Obviously, species native to your area will already be adapted to your local temperatures. Your state's Natural Resource Department may also have a say. In Georgia, for example, you can not grow Tilapia in any tank or pond that could potentially empty into any storm or runoff system. While it's not practical to list every possible stocking option, here are a few ideas:

  • Tilapia - These are the most popular fish to use world-wide because of their quick growth and ability to thrive in just about any system - as long as the water temperature stays above 70 degrees. Tilapia can also be stocked in ratios as high as one adult fish per gallon of water which is much higher than most species. Harvesting can be done in as little as eight months. As noted above, some states have restricted their use in outdoor systems. 
  • Catfish - Although slower in achieving edible size than Tilapia, catfish are an excellent choice. They tolerate much colder temperatures and are a native species in just about every state. Catfish require eighteen months to two years to harvest.
  • Trout - Trout are a popular choice, however, they require water temperatures below 80 degrees and constantly moving water for optimal growth. They require an average of 8 months to harvest.
  • Koi/Goldfish/Etc. - Non edible species are also usable if you are only wanting to fertilize your plants. 

While it's possible to directly filter the reservoir water through the root systems of your plants, your results will be much better if you include a bioreactor in your system. A bioreactor is simply a seperate tank filled with beneficial micro-organisms. These tiny little life-forms ingest the waste-stream from your fish stock and break it down into easily usable micro-and macro- nutrients. Maintaining a temperature above 75 degrees and keeping the water highly oxygenated are two important factors in keeping your bioreactor healthy. The size of your bioreactor should be equivalent to a tenth of your reservoir size, so a hundred-gallon fish tank would require a ten-gallon bio-reactor and would support a two-hundred-gallons of plant roots. 

We are in the final stages of construction on the greenhouse, a thirty foot diameter geodesic dome built from local bamboo and covered in greenhouse grade plastic sheeting. Although a bit labor intensive, the construction has gone smoothly. One of the unique things about building a geodesic dome is that you can construct it from either the top down or the bottom up. We chose the top-down technique so that we could attach the cover without scaffolding or ladders. When complete our dome will stand a little over 16 feet, so this was an important consideration. The cost of materials was about thirty-percent less than building a standard rectangular greenhouse, another important consideration. We got free plans and lots of information from the website which made our design and build much simpler. I highly recommend checking them out if you are interested in constructing any type of geodesic structure. 

Next month, we will dive into the hydroponics systems and vertical-gardening techniques. If you have any questions or private comments please feel free to write me in care of The Garden Enthusiast @ [email protected].