Aquaponic kit for a greenhouse, 6 or 12 vertical towers

The three ranges differ first of all in their pond size. Discovery, with 400 L, starts at 6 towers and goes up to 12 towers and 1 tub; it is for discovering aquaponics and growing the essentials, up to 200 kg of vegetables a year. Grow, with 600 L, starts at 6 towers and 1 tub and goes up to 12 towers and 3 tubs, for a versatile family vegetable garden producing up to 250 kg a year. Passion, with 800 L, starts at 6 towers and 2 tubs and takes up to 12 towers and 5 tubs, for those aiming at yield and variety, up to 300 kg a year.

Each model can then be expanded by adding towers and beds, up to the maximum capacity of its range, since the pond and the pump are sized for it from the outset. You can therefore start small and add to it after a first season, once you know your favourite crops. The choice comes down to two criteria: the floor area of your greenhouse, which rules out Grow and Passion below 7 m², and the share of large plants you want to grow, since it is the beds that take them. The larger the pond, the more fish it holds, and the more growing area it can feed.

Depending on the model, the pond holds 40 to 80 fish of 10 cm, to be ordered once the water has cycled. The guideline of roughly 1 L of water per centimetre of fish gives the animals room without isolating them, as too low a density encourages dominant fish to emerge. To start with, the comet goldfish, a hardy form of the goldfish, is the safest choice: it tolerates wide temperature swings and a pH of 6 to 8, and reaches about thirty centimetres as an adult. The guideline of 1 L per centimetre therefore needs recalculating as the fish grow, since a single adult goldfish needs 30 to 40 L of water on its own. Koi are also suitable, and edible fish can follow if you wish: carp, which are very tolerant, or trout, which are more demanding, suffer above 20 °C and are therefore harvested before the hot weather. The guide to goldfish in aquaponics gives the volume of water to allow per adult fish.

The kit includes all the operating equipment, for a total consumption of 60 W. The pump and filtration circulate the water continuously, and a silent oxygenator maintains the dissolved oxygen that the fish and bacteria need. A large-capacity automatic feeder, resistant to mould, dispenses up to 4 meals a day and holds up to 4 weeks of feed, so you no longer feed by hand. An automatic window opener regulates the greenhouse ventilation and helps keep a favourable temperature inside. Also included are a starter kit, with nitrifying bacteria, water tests and pH reducer, naturally sourced mineral salts for a year of growing, and a step-by-step installation guide and user guide. The pond itself is made of solid PEFC-certified wood, class 4 autoclave-treated, and is delivered with its liner and a protective underlay.

The kit arrives in 4 to 6 parcels of 20 to 30 kg, within 3 to 5 weeks, and can be assembled in a day, by yourself, with the installation guide; allow 1 to 2 extra days if you are also putting up a new greenhouse. The tools required are common ones: a cordless drill-driver, a 3 mm wood drill bit, 3 and 6.5 mm metal drill bits, a 10 mm spanner, pliers, a utility knife, a screwdriver, and a heat gun, which a hairdryer can replace. Then fill the tank and set the flow rate with clean water, without any fish. Once filled, the installation weighs several hundred kilos and cannot be moved without being emptied; so decide on its position at the time of assembly, leaving a path to walk along and access to the tank.

A new system contains no nitrifying bacteria, and without them the ammonia excreted by the fish never becomes a nutrient. So you fill the system, seed it with the bacteria from the starter kit, and wait several weeks before introducing any fish. The tests supplied show you the sequence: ammonium rises, then nitrites, then both disappear from the readings and give way to nitrates, the signal that clears the way for the fish. You can plant the towers while you wait. The biofilter then keeps building up and reaches full efficiency in about 6 months; starting in winter therefore gives you a mature system by the following spring. The guide to getting an aquaponic system started describes each step.

Maintenance comes to about 30 minutes a week, spread over a simple schedule. Every 2 weeks, you fill the feeder, check that the water flows normally in each tower, adjust the level and plant the next batch. Every month, you clean the filter, purge the valves, test the water and add the mineral salts according to the season. Once a year, you empty the towers, clear them of dead roots and put them back in place. The plants reach maturity in 5 to 8 weeks on average, so staggered successions let you harvest every week from spring to autumn. In summer, leave the greenhouse door open when it is hot, as water temperature is the parameter that deteriorates first; in winter, the fish slow down and eat less, and the pond water, constantly circulated, stays above 0 °C.

Once the system is up and running, it can grow within the limits of its range. If your height under the guttering reaches 175 cm, tower extension modules stack onto the existing towers and add planting positions without taking up any more floor space. Additional towers and beds can also be connected to the same water circuit, up to the maximum capacity of the pond. Every addition of planting positions means the feed input has to keep pace, since it is the feed that supplies the nitrogen: so leave the biofilter a few weeks between extensions, and check the nitrates before adding a new batch of plants.