Aquaponics /akwəˈpɒnɪks/: a system that combines aquaculture (the raising of aquatic animals) and hydroponics (cultivating plants in water) in a symbiotic environment.

Earlier this summer we were contacted by John Grant of Sheffield Hallam University to ask if we were interested in participating in his PhD research into the domestic application of aquaponics. We were, due to…

• Desire for water efficiency – aquaponics counter-intuitively is claimed to use a fraction of the water used in conventional food production
• Low maintenance – aquaponics offers automated water provision and no weeding
• Problems with slugs decimating conventional crops
• High yield and the potential to raise different fish
• Concern about soil degradation, and interest in alternatives
• Opportunity to reuse surplus food-grade IBCs

We are also able to test a system in a domestic setting, whilst also demonstrating it to visitors on our public and educational tours.

Site

John visited us in July 2016 to consider site options. The factors considered were:

• accessibility, as the system will need checking each day to ensure fish welfare
• orientation, to maximise light
• existing shelter, or potential cost of a new shelter
• access to water and power
• available IBCs, which had previously been used to store water on a smallholding.

The key factor was the availability of space in an existing polytunnel. This is about 200m from the homes and offers good light. Access to filtered water and to power had to be installed, and the challenge remains to stabilise temperatures to ensure fish welfare.

System design and build

Tank preparation 

Two food grade IBC tanks were used:

• one for the sump tank (700l) and one for a grow bed (300l)
• the other provided two grow beds

Cutting IBCs with a thin metal angle grinder blade proved surprisingly efficient and produced a clean smooth edge on the plastic. The alternative using a jigsaw would have been more difficult to control on the bendy sides and produced a rougher cut edge. There seemed to be the possibility of fine plastic dust created by the grinding although mostly the plastic melted when cut and a dust mask was worn to protect against this, along with ear defenders and goggles. The containers were swept and washed to remove this “dust”.

Measuring to create an accurate cutting line was difficult with the slightly rounded shape of the IBC. Best estimates need to be used.

Metal work cut easily and it took about 5 hours for all cutting of the IBCs. Creating a lid for the sump tank out of spare bits took about 1 hour. This minimized waste materials from adapting the IBCs.

Sump tank

Fish health and welfare is a key requirement and has driven the design. To keep the water cool, the sump tank has been sunk into the earth floor of the polytunnel. Whilst the temperature of the soil surrounding the tank will vary with the seasons, it will remain cooler than the air temperature in summer and warmer in winter. The degree of difference will be monitored and recorded as part of this project. There is the additional benefit of keeping the sump tank dark to prevent (or at least slow) algae growth. It was for this reason that we chose a dark tank, when initally we thought a light tank could be useful to mark water levels.

The main challenge with burying the sump tank is the pressure of soil on the sides of the plastic part of the IBC. This is averted to some extent by the use of metal panels in the centre of each side.

An inverted growbed was used to protect the sump tank whilst the soil was tamped down, as it protected the water from soil. This was then replaced with a lid, made from a timber frame and the ‘waste’ from the IBC that had been cut to provide two growbeds.

Fish tank

The fish tank is located over the sump tank. The factors considered as part of this decision are access to the fish tank, the simplicity of plumbing, and temperatures. These two tanks are placed next to the doorway with an area in which to put a small table on which to keep records for research. This area is slightly cooler than the centre of the polytunnel, and it is (in broad terms) preferable to give warmer temperatures to the grow beds and a cooler temperature to the fish tank.

The fish tank is offset so that dense concrete blocks can take the weight of the tank on 3 sides, and to allow access to the sump tank (allowing for the potential need to remove and maintain/replace the pump). This access is on the grow bed side of the sump and fish tanks to reduce the complexity of plumbing. The tank is being filled gradually both to limit impact on the availability of water to HHP residents, and to monitor the stability and level of the fish tank.

The fish tank is dark as this is the preference for the fish under consideration, but there is the risk that this will increase the temperature of the water. Another way to manage the temperature is to insulate the tank, and we are considering the use of sheepswool from the HHP flock.

Grow beds

The next stage is to install the grow beds. This needs to take into account:

• Accessibility for planting, including the rinsing of roots, and harvesting
• Plumbing – length and complexity; any impact on accessibility
• Shading of other planting areas

The two options considered were linear and keyhole.

Keyhole: a permaculture approach which minimises path to bed ratio, reducing the distance travelled to work on a bed. This has a particular value with aquaponics as plant roots must be cleaned prior to planting. Plumbing would be to the rear of the beds, with ease of access dependent on the distance of the beds from the polytunnel wall. Planters can be placed at the end of the paths, and potentially incorporated into the aquaponics system at a later date. Additional beds would be added in a similar fashion.

Linear: A more efficient approach in terms of materials used as plumbed routes are marginally shorter (the above diagram is not to scale). The pipework from the fish tank to the growbeds, and from the growbeds to the fishtank each have one less joint. It also allows for planting on a 20cm strip on the south of the polytunnel. The access path will need to be wider than for the ‘keyholes’ as it will need to allow for a working area to clean roots. Additional beds could leave a break to allow easier access to the south edge, with plumbing bridging any gap.

The impact on ease of use will only be fully understood from practice.