Guide written by:
John, Passionate gardener, Cambridge
Aquaponics is a centuries-old agricultural practice that combines fish farming and vegetable growing in a single symbiotic system. Thanks to recent innovations, the technique is now more accessible than ever. Read on to discover the benefits of aquaponics and follow our tips to get your system up and running!
- How it works
- Why choose aquaponics?
- How to set up your aquaponics system
Aquaponics: a symbiotic system for fish and plants
Aquaponics is an agricultural system in which the waste produced by farmed fish serves as fertiliser for hydroponically grown plants. The immersed plant roots, in turn, absorb toxic nitrates from the fish waste, purifying the water and allowing it to be safely recirculated into the fish tank as part of a continuous cycle.
The term 'aquaponics' is a contraction of the words aquaculture (aquatic animal rearing) and hydroponics (a water-based, soilless growing technique that is widely used for several types of plants). More than just an innovative way of growing vegetables, aquaponics is a path to autonomy that can help households and communities achieve greater food independence.
A farming method with ancient roots
Farming methods combining fish and plants can be traced all the way back to ancient civilisations. The Aztecs, for example, grew maize and beans on artificial islands made out of mud and reeds. The submerged roots would absorb the fertilising nitrates generated by fish waste.
Over 1,000 years ago, rice farmers across Asia used an ingenious canal system connecting rice paddies with fish farms. Modern aquaponics, born out of the 1970s energy crisis, improves upon these ancestral practices and adapts them for an urban setting.
And the concept is gaining traction worldwide. Commercial-scale farms are currently being tested in Europe, where aquaponics is just beginning to take root.
Aquaponics: how it works
A circular economy between fish and plants
Farmed fish raised in a pond or tank eliminate their waste directly into the water. Though toxic to fish if left unfiltered, this organic matter is rich in essential plant nutrients such as nitrogen, phosphorous, potassium, iron and calcium. And therein lies the key to aquaponics: this impure yet nutrient-rich water gets pumped out of the fish tank and into another nearby tank, from which it is dispersed over the substrate of a grow tray. Bacteria colonising the substrate convert ammonia from the fish waste first into nitrites and then into nitrates. This process creates a nourishing base from which the plants will absorb nitrates and other minerals present in fish waste. Once all toxicnitrates have been removed from the water, it can be safely recirculated into the fish tank. And that's aquaponics cycling in a nutshell: a closed-loop system that cycles water from fish tank to plant bed and back again. The same water that serves as a habitat for the fish also constitutes a nutrient-rich source of nourishment for the plants. Aquaponics takes the principles of a circular economy – in which the waste produced by one system becomes a resource utilised by another system – and applies them to food production. That philosophy is the very basis of permaculture.
An aquaponic farm is essentially an artificial ecosystem in whichthree key players interact:
- fish, whose waste contains high levels of ammonia;
- cultivated plants, usually vegetables, whose roots absorb nitrates and other minerals essential to healthy growth;
- bacteria, which acts as a buffer between fish and plants, converting the toxic ammonia from fish waste into plant-nourishing nitrates.
Why choose aquaponics over traditional farming methods?
In 2017, the European Parliament published a report acknowledging the enormous potential of aquaponic farming, given its numerous advantages over traditional farming:
- Aquaponics uses much less water than traditional intensive farming – up to 95% less according to many proponents of the method!
- Since aquaponic plants get a steady supply of nutrients and oxygen delivered directly to their roots, vegetables grown aquaponically will grow 2 to 3 times faster than in traditional farming.
- For that same reason, aquaponic farming allows for greater crop density: direct and steady nourishment means less competition for space among plants, since they don't need to extend their roots far to find nutrients.
- Unlike traditional farming, aquaponics produces two different food sources: vegetables and fish. Many – though not all – types of fish are well suited to aquaponics.
- Aquaponics yields superior-quality vegetables, comparable to organic soil-grown vegetables in terms of flavour and nutrients. Indeed, just like in traditional organic farming, no chemical fertilisers or pesticides are used in aquaponics. And of course, no pesticides = no pollution.
- Unlike traditional growers who have to crouch down or hunch over to tend their plants, the aquaponist works in a more ergonomic upright position. So, say goodbye to your spade, hoe, garden hose and weed trimmer (there are no weeds!). Aquaponics is, accordingly, perfectly suitable for anyone with a physical disability or impaired mobility.
- Aquaponicscan easily be practised in an urban setting – no farmland required!
- Soilless growing also eliminates the risk of crop damage from burrowing animals and insects like moles, voles or mole crickets.
Aquaponic farming: the ecological way to grow
Aquaponics also has a number of indirect benefits. For one thing, it exemplifies the eco-friendly farm-to-table trend by favouring local, direct sales channels and thereby keeping transport costs and CO2 emissions to a minimum. Moreover, no soil means no fuel-guzzling tractors, tillers or other motorised equipment – and that also means less pollution.
Aquaponics could even help foster greater food independence among isolated populations, i.e. inhabitants of remote islands.
Aquaponics: the best method for beginners
A number of variations of the practice exist, the one common denominator being a soilless, water-based farming technique known as hydroponics.
The media-filled growbed method
The most popular method for small-scale, household aquaponics systems uses what is known as a media-filledgrowbedor MFG. In this case, the goal isn't so much quantity as variety.
In the MFG method, a grow tray is lined with an inert, neutral substrate, such as expanded clay pellets or gravel, which will serve as both a base and a growth medium for the plants. Water from the fish tank can be pumped into the tray on a continuous or intermittent basis. In the latter case, known as the 'flood and drain' method, a bell siphon is used to regulate ebb and flow.
Getting started: four steps to a thriving aquaponic farm
1. Setting up your tank, grow tray and pump
Spring is the ideal time to set up your aquaponics system: warmer temperatures (optimally 25-30° C) will help speed up the bacterial growth process.
The two main components of the system are the fish tank (or pond) and the grow tray. As far as size is concerned, your ambition is the limit, but if you're new to aquaponics, it's best to start small. Remember, you can always expand as you go along! The other crucial component is the pump, which drains water out of the tank.
2. Testing the components and water cycling
Before permanently installing the different parts of your system and adding your fish and plants, you need to make sure that the mechanical components function properly.
- To do so, start by filling the highest unit of the system; this is usually the grow tray.
- Next, drain the water down to the level of the next highest unit, usually the fish tank.
- Now, connect the pump and calculate the pump flow rate. To do this, you'll need a 20-litre bucket or other pre-measured container. Keep in mind that the tank water should be cycled once or twice per hour.
3. Cycling and monitoring your water
Cycling an aquaponics system means harnessing bacteria to set the nitrogen cycle in motion, as briefly mentioned above. This process can take about 4 to 6 weeks, depending on the water temperature. The rules for cycling aren't set in stone: some degree of trial and error is necessary, but proper organisation and precision are key.
To get started, you'll need to purchase a water test kit, typically used to measure water quality in aquariums. The test, which is very easy to perform, will give you the water's pH as well as levels of toxins like ammonia, nitrites and nitrates, which could be deadly to your fish.
Once you've verified the water quality, you can start running the pump.
To get the cycling process going, you need a catalyst. As counterintuitive as it may seem, the best catalyst is ammonia. There are a number of ways to add ammonia to your system. Here are two suggestions:
- addpure ammonia, which you can find at your local DIY shop under the names 'pure household ammonia' or 'pure ammonium hydroxide'. Check the label to verify that no additives (i.e. scents or dyes) are present.
- add fish feed to the fish tank (but don't add the fish just yet!). As it breaks down, the feed will release bacteria-nourishing ammonia.
Gradually introduce small amounts of your preferred ammonia source until you get an ammonia reading of 2 ppm (or 2 mg per litre of water). Be careful not to exceed 3 ppm. Repeat this step every day, adding the same amount, until nitrates appear, a sign that the nitrifying bacteria are doing their job. Once ammonia levels have dropped to 0.5 ppm, you can halve the daily dose.
Keep in mind that, since these bacteria are naturally present in the environment, theywill colonise the aquaponics system all on their own. That said, you can speed up the process by actively introducing bacteria into your aquaponics system. Simply take a piece of filter media from an existing aquarium or a bit of substrate from another aquaponics system and add it to your own system. If you don't have access to either of these bacteria sources, you can use a nitrifying bacteria starter kit to speed up the cycling process.
Now, test the water once again to verify that pH levels are within an acceptable range (the optimal pH range depends on the type of fish you are raising). If the pH is too high or low, very gradually add small amounts of pH-adjusting solution until you reach the optimal range.
4. Adding plants and fish
Once enough nitrates have built up (aim for 5 to 10 ppm) and nitrite levels have dropped to 0 ppm, you can add your plants to the grow tray. They will immediately begin absorbing the nitrates from the water. At this point, you can add your fish. Aim for around 20 goldfish for 100 litres of water.
Choosing your fish
The hearty goldfish is a good starter species as it is quite forgiving of beginners' mistakes.
Opt for floating small-pellet feed (1 to 2 mm) over flaked feed.
Choosing your plants
As for vegetables, it's best to start with easy-to-grow varieties that will thrive on a steady supply of nitrates: think leafy vegetables like lettuce, spinach and chard.
But the list doesn't stop there. Aquaponists grow all kinds of plants, from herbs (basil, parsley, coriander, mint, chives) to tomatoes, cucumbers, strawberries, flowers and beyond!
Filter media from an existing aquarium
Guide written by:
John, Passionate gardener, Cambridge, 57 guides
When I was young, I was already working in the family garden. Perhaps that is where my interest in plants and gardening came from. So, it was logical for me to study both plant biology and agronomy. At the request of various publishers I have, over twenty-five years, written many books on the subject of plants and mushrooms (a subject that is close to my heart).They were mostly identification guides at first, but shortly after they were about gardening, thus renewing the first passion of my childhood. I have also regularly collaborated with several magazines specializing in the field of gardening or more generally in nature. There is no gardener without a garden, I have cultivated mine in a small corner of Cambridge for the last thirty years and this is where I put into practice the methods of cultivation that will I advise you in as well.