RDWC PRO hydroponic kit, 3 to 24 buckets

The shared controller pot means that an RDWC is run differently from a row of independent pots: all the pots share a single solution, which you adjust once. In return, a dosing error spreads everywhere within minutes, which is why an electronic pH meter belongs next to the controller. Measure before correcting, then measure again half an hour later: between the two readings, the pump has redistributed your correction throughout the network. This pooling also requires all your plants to be at the same stage, because a plant in flower and a young seedling connected to the same circuit receive a compromise solution that suits neither. The solution temperature is monitored in the same place: above about 24 °C, the water holds less dissolved oxygen, while the submerged roots consume more.

A 19 L pot in which the roots sit in oxygenated water is very similar to a deep water culture grow bed in aquaponics, and the network can be connected to a pond. Two things then change. You lose the freedom to make corrections, because the pH range that suits plants is not the one that suits fish and nitrifying bacteria, which is the main difference between aquaponics and hydroponics. On the other hand, you gain a considerable buffer volume, which smooths out variations in pH and temperature better than a channel does.

The second point is mechanical. The water from a fish tank carries suspended solids that the in-line filter is not sized to handle continuously, so mechanical filtration upstream becomes necessary. The nitrogen cycle takes place before the pot network, in the tank and in the biological filter. In practice, such a set-up therefore calls for a settling tank and a biological filter sized for the fish load, and the RDWC network only comes afterwards, at the end of the chain.

The ten configurations can be compared by floor area as much as by number of plants. The 12-pot format is the only one available in two layouts, three rows or four rows: both take up a similar floor area, and what changes is the position of the controller pot, in the middle of a short side for the three-row layout, and on a long side between the rows for the four-row layout. So work out which side you will reach the controller from before choosing. The 16, 18 and 24 formats call for a dedicated room and access to water, otherwise topping up by hand becomes a daily chore. In every case, allow a gap of at least 60 cm on one side, so that you can reach the controller and rinse the filter without moving a full pot. Finally, choose the number of pots according to what you intend to grow: each 19 L pot holds one fully developed plant, such as a tomato or pepper, which needs its space above the pot and its staking, and the pots should be placed 50 cm apart.

You receive the grow pots, the controller pot with its lid and valve, the inline filter, the two pumps, one air stone per pot, and the 50 mm pipework with its elbows, seals and drilled lids. Nothing needs gluing: the push-fit fittings clip together by hand, and you can assemble and dismantle an entire network without picking up a tool. This is what allows you to change configuration between two cycles, by draining the circuit, adding or removing a pot, then refilling straight away, without cutting or re-gluing anything. It is made in Italy, and the pots keep the range's double wall, black on the inside and white on the outside. The inner wall keeps the solution in darkness, which deprives algae of light, and the outer wall reflects the radiation from the lamps, so the solution heats up less in an enclosed room.

Three families of parts need replacing as the seasons go by. The 50 mm push-fit seals lose their elasticity after repeated dismantling and eventually start to weep. The cylindrical air stones clog up with mineral salts and can be recognised by their large, irregular bubbles. The 14 cm baskets crack when you pull out a mature plant with too much force.

A cracked pot, on the other hand, cannot be repaired: polypropylene does not glue back together cleanly, so the 19 L grow bed is ordered on its own. The rest of the system can be taken apart and reassembled without tools, which means a PRO can be reconfigured between two cycles rather than replaced.

A network of 6 pots holds 112 litres of solution, or roughly 16 litres per pot, to which you must add the weight of the pots, the wet grow medium and the plant, which brings a network of 24 pots to around 500 kg spread over a few square metres. The floor therefore needs choosing before the first filling: a slab, a load-bearing floor or tiles will do, whereas an old parquet floor or a board on trestles is much less suitable. All the pots must also sit at exactly the same level, to the millimetre, since only gravity equalises the water heights between them: a pot wedged slightly high receives less solution than its neighbours, and you will see the difference on the plant before you see it on the water level. Running a spirit level under each pot during assembly saves you that search weeks later.