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How does aquaponics work?

Updated: Jan 30, 2021

Self-sufficient, sustainable growing, made easy

How does aquaponics work?

Aquaponics is the joining of hydroponics and aquaculture. It is a dual raising system which grows both fish and plants organically, without the need for weeding, watering or spraying. It can produce hugely increased yields with a fraction of the input compared to conventional growing techniques.

Here at The Aquaponics Project we think that the best way to explain how it works is to look at it as a cycle of nutrients. Aquaponics harnesses the power of the Nitrogen Cycle from fish to plants in a symbiotic process. In our explanation we will follow the flow of water from the fish tank, through various filters, to the plants, and back to the fish again. This simple diagram summarises the process:

Rather watch it than read about it? Click here for our ‘What is Aquaponics’ lesson.

Step 1: The fish introduce the ammonia.

As a natural waste product fish produce ammonia. Fish, as with other vertebrates, excrete their waste through the digestive tract, skin, and especially, the gills. This would otherwise be fatal if it built up in their systems. It is for this reason that it is important to keep track of the ammonia levels in your fish tank. Ammonia levels can also build up in the tank from decomposing fish food which is not eaten. We will look at the topic of optimum conditions for fish in a future blog, however this site by the Trout Unlimited offers a good overview. We recommend a maximum level of 9ppm of ammonia to keep your fish healthy.

Step 2: The ammonia leaves the fish tank

The Ammonia rich water is sucked out of the tank along with any decaying solid matter such as uneaten food and fish excrement, transporting it to the Solids Filter.

Step 3: The Solids filter

At this stage the water is heavy with dissolved ammonia but also carries with it a lot of solid matter which would otherwise clog up the system. There are a number of different filter systems available. The Aquaponics Project systems employ a swirl filter. The laminar flow of the water allows the solids to settle at the bottom of the filter.

The solids can easily be drained, usually on a weekly basis. This creates a completely organic and highly concentrate fertiliser which can be used in standard soil based gardening. By the time the water leaves the filter nearly all the solid particles will be gone. In a healthy, mature, aquaponics system it will still have high levels of ammonia, ready to be converted by the next system.

Step 4: The Biological filter

At The Aquaponics Project, for our largest system, we use an additional biological filter to increase the amount of minerals available to the plants. Whilst this is not necessary for healthy crops it does increase the speed at which plants will grow (as well as their size) and therefore the system’s annual yield.

If it is the fish that are providing the fertiliser for an aquaponics system, it is undoubtedly the biological filter (and media bed which we will discuss later) that is the engine room of any system. Within the Garden System’s Biological Filter are K1 media. These have a massive surface area of 280 ft2/ft3. In a future blog we will look at the importance of biological surface area in a system in more detail. Essentially this is the area that the bacteria have in your system to cultivate. There are two colonies of bacteria that are essential to all systems. The first colony will convert the bacteria from ammonia into nitrites. The second colony of bacteria converts the nitrites into nitrates. Your plants will grow by absorbing the nitrates through their roots.

The bigger the surface area available, the more bacteria that will colonise your system and the more ammonia your system can convert into nitrates. It is for this reason that The Aquaponics Project’s Garden System complete with Biological Filter will grow crops faster. The filter provides more nitrates for the plants to grow.

It is important to remember that while these two bacteria are naturally occurring in the air (and therefore completely free), they do need time to colonise your system. In our tests this takes around 40 days. As we can see from the graph below, after the introduction of the fish the ammonia levels spike around day 10. From around day 4 or 5 you can begin to detect traces of nitrites in the system which shows the first colony of bacteria have arrived. Shortly after this the second colony of bacteria arrive and begin to convert the nitrites into nitrates. The nitrite levels spike around day 20 but by day 40 the levels of ammonia and nitrites will be negligible. At this stage you will have an efficient system.

Step 5: The Media Bed

From the biological filter the water will be charged with soluble nitrates, ready to be absorbed by the plants roots. It is only The Aquaponics Project's Garden System that has the option of an additional Biological Filter. The reason for this is that the benefits of a biological filter in smaller systems are not so great. This is because in smaller systems the media beds themselves provide enough surface area for the bacteria to colonise. The Aquaponics Company Media Beds use Hydroton which has a surface area of 70 ft2/ft3.

Our Home System and Balcony System both are fitted exclusively with Media Beds. This is where your plants will grow. The added benefit of a media bed system is that you can grow taller plants which require a more solid root base.

Another ingenious piece of engineering, the bell syphon (Step 5a), ensures that your plants have the correct amount of water, while the bacteria have access to plentiful supplies of oxygen which they require to do their job. The water fills to a certain level within the Media Bed before being sucked out again.

Step 6: The DWC

Water leaving the Media Beds will still retain a lot of its soluble nitrates. It is for this reason that we recommend adding a Deep Water Culture system. These are large pools of water upon which float rafts which contain your plants. As they do not contain any media (such as the Hydroton in the Media beds) they are a considerably more cost effective way to grow plants in your Garden System.

An additional two Deep Water Culture systems can be added to our Garden Systems if a Biological Filter has also been added.

Step 7:

From the Deep Water Culture the water makes its final journey to the Sump Tank. Up to this stage, in our Garden System the flow of water has occurred entirely through gravity. In spite of its name, the sump tank should contain the purest water in the system. It has had all of its ammonia, nitrites and nitrates removed and sits at the lowest point in the system. From here a water pump takes it up into the fish thank. The output of this water pump is particularly important as it needs to be powerful enough to replace all of the water in the tank every hour.

Although we have not experimented with it yet at The Aquaponics Project some aquaponics enthusiasts have managed to create a completely closed system, growing pond weed in their sump tanks which they can then use to feed the fish.

Aquaponics, in essence, is a really simple system. Here at The Aquaponics Project we firmly believe it is the future of farming, be it on a larger commercial scale, on a small self-sufficient level, or, and this our favourite, a mixture of both. In order to show just how simple and beneficial the system is we have summarised it into this concept map

AWR 2020

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