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Full view of greenhouse, NFT, and big pot.

So, it has been a long few months of building, then a longer few months getting the water quality to stabilise, but its finally working! 1000L fish tank, ~100L sump (i.e. a bathtub), 120 little pots, 1 big pot (with a makeshift float valve), some DIY drip irrigation and a bunch of happy plants.

Some insights

  • A biological filter (bio-filter – i.e. some crumpled up shade net in an old pool filter) makes for a good bacterial home, but is still not good enough to settle out the solid waste. A two stage filter is definitely a must.
  • Using 110mm PVC pipes in this configuration (i.e. Nutrient Film Technique – NFC) makes for an excellent solids settling zone. Not so great for root health though.
  • Algae reduction mechanism is not completely known, but getting the nitrifiying bacteria population up and running in the bio-filter was likely the culprit.
  • Adding and active population of Egeria densa with some aquatic snails seemed to accelerate water stability and algae reduction.

A walk-through of the build

This scale-up of my aquaponics prototype has been an interesting build to say the least. Using mostly parts from old projects (flowbins), a steel frame used on one of the old bakkies, a couple of old bathtubs, and an old pool filter (without the sand) and part of an old garden in a plumbing business’ yard, I made an aquapoincs system to grow a variety of plants. Some new parts were required: a fountain pump, air pump, two aquarium heaters, a makeshift roof (shade net), piping, valves, and associated connections and reductions. A concrete slab with a small retaining wall was also needed to hold the tank. Lets step through the process of putting it all together.

Preparing the site & planting areas

Planting & stabilising the water

After months of waiting and trying to stabilise water using different aeration, water cycling and planting strategies, the water finally stabilised after the addition of a floating plant (Egeria densa) and aquatic snails from my smaller fish tanks. There is still some doubt whether the water quality would have stabilised eventually by itself, but I have been reading a lot and there are many factors that can lead to stable water. Since I cannot do water quality measurements yet, I have to do it by eye and intuition. The success of E. densa in the tank leads me to believe that the addition of these plants helped slow down water flow, settled the algae, intercepted some light, and reduced nutrients in the water. The snails ate any remaining algae and turned into nice solid waste that could more easily settle. Once the bacteria in the filter got up and running, the solid waste breaks down and gets fed to the plants and then I got some healthy growth happening.

Improvements

This system took way longer than I expected to stabilise and to see good growth. A second stage filter to help with the solid waste in the NFT seems to be a necessity. Making the solid waste accessible for other uses would be a big plus too. The drip irrigation could be improved as the dripping was uneven, the DIY side of things has its pros, but this is definitely a con. The growth in the garden bed was amazing and I see a lot of potential in drip feed irrigation from aquaculture waste water (see Fertigation). The balance of fish to plants also could be improved, but with the recent rains, and less water changes, I am getting good growth all round. My thinking is that more plants of different types, as well as integrating more organisms like giant river prawns, in addition to Tilapia would make the system more productive and more resilient to changes and disease. 

To improve the stability of the water, either I would need to purchase microbes to inoculate the system, or figure out how to take from my existing aquaponics systems. I think some of the growth media could be a good inoculum, but it would mean getting enough of the medium together to make sure the system is inoculated quickly, or at least faster than a few months.

 

Future work

Now that I have a larger prototype and I have spoken to a few people, the next challenge is getting a salable product. All the nuts and bolts, services, and possible sizes of custom system formed into a product. Finding suppliers for tanks, fish, plants, sensors, feed, pro-biotics and more. Integrating these systems, getting feedback and making this system as simple as possible are key considerations for me right now.

The conversations I have had with other small business owners seem to point to high prices, expertise, and low value of products as some limitations of aquaponics in South Africa. However, our agricultural sector is very large and many products are available for agriculture in general. As more awareness of diverse sets of products improves so will demand. Some exciting areas that are emerging are medicinal plants, biogas, algae, and turning waste into value (the circular approach to production). Many different technologies are emerging that I hope to cover in future posts.