Myfood City balcony aquaponics greenhouse, 3.5 m²

The 300 kg of the bare greenhouse is spread across its footprint and should pose little difficulty; it is the further 400 kg of water and crop added afterwards that needs a clear answer. The ground must be flat and level, a condition for the ponds to work properly, and the supplied slab plan includes a slight slope towards the back so that rainwater can drain away. Moving the greenhouse remains possible as long as it has not been filled with water, and the freestanding structure can be taken down completely and re-erected elsewhere; keep the glass packaging if a move is planned. With a footprint of 3.56 m², the City also stays below the 5 m² threshold above which prior notification of works is generally required. Choose the final location with sunlight, access to a socket and a water point for topping up in mind, and keep access to both sides so that you can harvest and open the pond.

In a vegetable garden, you decide everything: when to water, what to fertilise, when to add soil improvers. Here, your main lever is feeding the fish, and everything else follows from it: the towers receive what the 300 L of pond water produces. An under-stocked greenhouse gives pale plants, and an over-stocked one raises the ammonium level before the bacteria catch up. For a greenhouse of this size, the rule of 40 to 50 g of feed per day per square metre of growing area leads to a ration of a few tens of grams. In a small volume, this adjustment is felt more quickly than in a large installation. A weekly check is then enough to keep it on track: ammonium and nitrite stay undetectable, and the pH stays between 6.4 and 7.5, a compromise between fish, bacteria and plants.

A submersible pump rated at 5,500 L/h and 50 W circulates the pond water to the top of the towers, from where it falls back by gravity through the roots. A 300 m³/h electric fan stirs the air under the glazing. The whole setup draws less than 70 W from a 230 V 50 Hz socket, so you do not need to change your consumer unit to install it. The circuit runs continuously, including at night, since nitrifying bacteria need permanently oxygenated water. As for water, allow around 3 m³ of top-up a year, or 1 m³ if you fit rainwater collectors, depending on the climate and how much the plants consume. A pump with this flow rate needs cleaning once a season, as its filter catches detached roots and fine grow medium particles that would otherwise end up reducing the flow in the towers.

The 300 L of pond is the source of nitrogen for the whole greenhouse: the fish load the water, the bacteria convert it and the towers consume it. A volume of this size warms up and cools down faster than a garden pond, which dictates the choice of species. For your pond, aim for a hardy ornamental stock that tolerates temperature swings, rather than a species that demands water held to the exact degree. Count the load in kilos rather than in number of fish: the ceiling of 20 kg per cubic metre used in small-scale aquaponics works out at 6 kg in 300 L, and half of that is enough to begin with. The article on fish to raise in aquaponics compares the species, and the guide to the nitrogen cycle explains what happens between the pond and the towers.

The City comes in three versions, and you choose between them according to the equipment you want. The Originale brings together the essentials: the bioclimatic greenhouse, the aquaponic system, a starter kit and access to the mutual-support community. The Production adds a comfort module and two permaculture beds. The Signature goes further still, with an infrared-heated winter module, a wooden floor, water collectors, the 4-tower extension and the connected unit. This unit, which sends the temperature and pH over Wi-Fi or the Sigfox network, can be added as an option on the Originale and the Production, and is fitted on each of the three versions. The article on outdoor aquaponics greenhouses and kits compares the two approaches and their budgets.

A new pond does not yet hold any nitrifying bacteria, and the colony takes 3 to 5 weeks to establish: ammonium peaks first, then nitrites, and nitrates take over once these two compounds can no longer be measured. The first fish arrive only at that point, in small numbers. Test every 48 hours to follow this cycle, then weekly once the pond has stabilised. You can plant the towers as soon as the pond is filled, as the plants grow slowly at first. The guide to getting an aquaponic system started details the steps up to the introduction of the fish.