Last month we focussed on the bacteria system as the crucial element in aquaponics to form a complete ecosystem with the fish and plants. It is very important for an aquaponics system to remain in balance to create optimal conditions for health and growth.
The system is in balance when the ammonia released by the fish is changed into nitrites and nitrates by bacteria, and when there are enough plants to absorb and use up the nitrates before the water goes back to the fish. This happens when the number of fish and plants are in balance and the bacteria had enough time to do their work. This process is called: Cycling up.
When starting a new system, this process can take weeks, depending on the size of the system. In the chart below this balance or “sweet spot” is reached where the blue and green lines cross:
The question most new aquaponic growers struggle with is: How many fish do I need for how many plants and how big must my fish tank and grow area be?
Unfortunately, there is no easy formula – because fish and plants both grow. Bigger fish release more ammonia and give more nitrates. Smaller plants need less nitrates. You can’t only use the number of fish or plants as a basis; it is more accurate to use the quantity of fish food needed as
the starting point of your calculations. Inevitably you give less food to smaller fish. Tilapia eat about 1% of their bodyweight per day. In other words, a 100 g fish eats 1 g fish food and a 1 kg fish eats 10 g fish food daily. You can determine the amount of fish food needed by weighing 10 fish and calculating the average weight.
The formula determining the balance between fish and plants was worked out by Dr James Rakocy of the University of the Virgin Islands, who developed the well-known UVI aquaponic system. It is the first commercial system based on scientific studies. The formula was later refined by a colleague of him, Dr Will Lennard. The formula we use is: 20 g/m2/day. That means you need to feed 20 g of fish food per day to enable 1 m2 of growth in a raft system.
The guidelines are:
• Decide how many plants you want to grow – for example 30 heads of lettuce (1 m²).
• If you want to plant 30 lettuce plants, you need 20 g of fish food – that means you need 2 kg of fish.
With all of the theory and biology in your head, it is time to start building your system. For a basic design you will need the following: A fish tank, something to remove the solids, a bacteria system,
the plants and a sump for the water to flow in. The Kleinskuur system also includes a process to mineralise the solids for added nutrition. At the top is the basic system and at the bottom the Kleinskuur variation with mineralisation included in the water flow (Figure 2). From the fish dam the water should flow with gravitation through the rest of the system until it ends up in the sump from where it gets pumped up to the fish dam again.
The components you need for a basic system:
• Fish dam/tank
• Conical tank with stand for swirl filter
• Nitrification tank with media for bacterial growth
• Gravel bed(s)
• Deep water culture bed(s)
• Pipes and fittings
• Water pump
• Air pump
The UVI system only uses deep water culture (no gravel beds), but that means you have to clean out filters daily. See Figure 3. Murray Hallam is an Australian expert who expanded on the basic UVI design by adding gravel beds as seen in Figure 4. His system is known as FloMediaTM and he sells his plans online.
Many people try to do their own thing, thinking if you put some fish and plants together and pump the water through the system, you have an aquaponic system. It is not that simple and you need to do your homework and sign up for a proper course, especially if you want to make a living out of it. How big you go depends on the purpose of the system. If you just want to feed your own family you will need a growth area of about 6 m x 6 m. If you want to grow for a community, think in terms of a standard 30 m x 10 m tunnel. If you want to farm commercially and make money from the produce you are selling, you need to compete with other commercial farmers who plant in soil.
These are the questions you need to ask yourself before you start building:
• Goal: What do you want to accomplish? Do you only want to supply yourself and your family with healthy produce, is it a school project, do you want to uplift a village, or do you want to compete on the open market and earn money?
• Choose what you want to do, because the design of your system will depend on your needs. Choose between: Home system, semi-commercial or commercial.
• Space: How much space do you have? For a home system feeding 4 people 36 m2 should be enough; to earn money you need at least an area of 80 x 60 m.
• Location: Does the area get enough natural sunlight, on which hide of the mountain are you, are there tall buildings or woods around you, is hail (or snow) a problem, do you need to tame the desert or clear the bushveld before you can start?
• Water: Do you have access to clean water? It should rather not be city water or run-off from the local mine. Although you use a lot less water than in a conventional system, you still need to fill
the system. Make sure you have enough water.
• Budget: Plan your development in such a way that you do not run out of money before you start getting an income. Don’t think that you will be getting BIG money without first putting in some BIG money. It can also be a lot cheaper to build a home system than you think, if you are handy and creative in finding your own solutions. Prepare yourself for a cost of around K20 000 for a home system and easily up to K2,5 million for an economical size commercial system.
• Market: Who is going to buy from you? How far are you from your market? Do you need to transport your goods? Can you supply supermarkets? FIRST DO YOUR RESEARCH IN THIS REGARD BEFORE YOU START ANYTHING!
• The future: Where do you want to be in ten years? Perhaps you want to start small and build up to a huge system or multiple systems. Plan and build in such a way that your foundation is there if you want to expand.
• Business plan: Compile a proper business plan. After your capital expenditure for building the system, you will face other expenses such as rent, electricity, water, wages, office expenses, internet
and telephone, transport and vehicle costs, insurance, bookkeeping, packaging, refrigeration, fingerlings, seed and especially fish food.
The beauty of aquaponics is that once you start producing in a proper system your yields will be much much higher than in any other system without having to resort to chemical fertilisers and pesticides, and you will never have to weed!
Hallam M., Practical Aquaponics, Master Class Training Manual, 2015
Bremner CD. & Bremner A., Introduction to Aquaponics, Training Manual, 2017