Design: Scale and layout.
Once again, welcome back to my fortnightly DigiLetter, 'Aquaponics: The Definitive Reference'. In this issue we will embark upon the most important part of any aquaponics journey — the initial design process itself.
Design:
When designing and building aquaponics systems, one piece of wisdom is to be remembered above all and kept foremost in your mind. It is known as the 'K.I.S.S.' principle:
Keep It Simple, Stupid.
Continuing with my tradition of quoting Wikipedia at least once per issue, “The KISS principle states that most systems work best if they are kept simple rather than made complicated; therefore simplicity should be a key goal in design and unnecessary complexity should be avoided”.
The intended longevity of an aquaponics system is what makes this particular design principle so important. Over the years I have witnessed thousands of design variations on aquaponics. While many design 'improvements' may appear constructive and useful on the surface, only very few amount to actual long-term positive and desirable benefits. Generally speaking, the simpler design alternative is almost always the preferable one. Unfortunately, most of the designs available on the internet lend themselves towards long-term maintenance problems. What makes aquaponics exceptionally difficult for a beginner is that like most things, you can only know by having designed, built and managed many different types of systems over many years. Auto-siphons are the ultimate example. Despite the fact that there is a simple, cheap and more reliable alternative (i.e. simple timers and a permanent drain, as described below), something along the lines of 80% of new systems appear to be designed with auto-siphons. Here I shall endeavour to demonstrate only the most efficient methods that I myself use.
Scale:
The first task is to decide whether your system will be indoor or outdoor. This will be the determining factor in how big or small your system will be. For a new system, the rule-of-thumb to follow is to aim for a 1:1 ratio of grow-bed to fish tank volume — a 100 litre fish tank needs 100 litres of grow-bed. Don't worry if you can't quite manage that right away – half (0.5:1) is enough to start with and you have at least a few weeks time to build up the biological load before a 1:1 ratio becomes a requirement. Mature and heavily stocked systems can require as much as double the grow-bed to fish tank volume (2:1) and additional bio-filtration — however no aquaponic system should ever be started out 'heavily stocked'. Grow-beds can be added later as the fish grow and the biological demand of the system increases.
Grow-beds should be at least 350mm (14 inches) or deeper if there is no other bio-filtration planned (more on that next issue). This depth allows for our microbes to fully escape the light that they hate so much, while also providing sufficient space for their required population. For various reasons, you should build the biggest system you reasonably can. One of those reasons is that the larger the system is, the more temperature-stable it will be. Another is that the larger the system is the easier it is to maintain water quality.
If you live in a climate where snow settles on the ground every year for a week or more — or your minimum annual air temperature is much below -4 Celcius (25 F) — then you may want to consider an indoor system. Water temperatures need to be kept high enough for both the microbes and the successful growth of the plants. Water temperature below 10 Celcius (50 F) is approaching survival-mode for most edible crops and, even more importantly, for our precious microbes.
An indoor or 100% covered system might be inside your house itself, but it could also be in a greenhouse, a shed or any external structure. Clearly the greatest limitation of indoor systems is the lack of sunlight. Greenhouses go some way towards mitigating this, but they still limit plant photosynthesis. LED grow-lighting is the only realistic solution to indoor growing. Using power-efficient LED grow-lights alongside natural light increases the overall photosynthesis and assists with enforcing seasons. By only using the LEDs to augment natural light and natural seasons (instead of using them strictly for intensive growing), a lot of power and money can be saved and a larger area can be serviced. As a result, for serious, large projects in cold climates probably the best solution is a system entirely inside a greenhouse with LEDs to compliment natural light. An active compost heap inside the greenhouse can help provide warmth and CO2 to the plants.
An outdoor system can be as large as a property itself. Just as an example, the largest vessel I have seen that was suitable as an aquaponics fish tank (a HDPE water tank) was 4600mm (15 ft) in diameter. At 1000mm (3.3 ft) deep this makes for a 17,000 litre (4500 gal) fish tank. At 350mm deep and 1000mm wide, this would require 50 meters of grow-beds and provide 50 square meters of planting space. This can grow to 100 square meters as the system matures and stocking density increases. Remember – the grow-bed area is just the planting area. The actual area that the plants can occupy is more than double that again. Commercial set-ups with even larger requirements can simply begin repeating and replicating this maximum size.
Layout:
Firstly, just like the auto-siphon we will do away with another common design addition that is actually just another unnecessary complication – a sump. The only semi-valid reason for considering using a sump is to ensure that the water level of the fish tank is kept at an exact and consistent level. To put it simply, this is unnecessary. Cyclic changes in maximum water level of less than 15% are completely acceptable and such minor variations are of no concern to the well-being of the fish – especially at depths of up to a meter. If it were, fish would be a lot less inclined to rise and fall in the water column voluntarily, as most fish do. Once again, this understanding and acceptance allows for simpler and therefore more resilient designs.
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