Gentle nutrient solution for seedlings and cuttings

Formulex is a synthetic mineral fertiliser intended for pots, propagators and hydroponic systems without fish. You should therefore never pour it into the pond water, as it would add salts the fish do not need, and its pH, buffered at around 6, would pull the water below the 6.4 to 7.5 range where nitrifying bacteria and plants find their compromise. It belongs upstream. A seedling in a cube or a cutting rooted in a cutting propagator will benefit from those first two weeks of gentle nutrition, then move on to the grow bed, where the fish waste takes over. Simply rinse the root plug in clean water before placing it in the system. The article on successful spring seedlings covers this step in detail.

In a so-called decoupled system, the fish water does not return to the pond after passing through the crops: it is pumped to a separate growing loop that works like a hydroponic circuit. This separation lets you adjust nutrition and pH for the plants without exposing the fish, an approach developed by European aquaponics research to reconcile the needs of the two compartments. You can then use Formulex to top up the rearing water in the plant loop only, for example on a table of seedlings or cuttings. This use assumes that no water from this loop returns to the pond, and that its drain goes to the garden or the wastewater system.

Fish feed supplies most of the nitrogen, but an aquaponic system most often runs short of iron, potassium and calcium, three elements that fish waste provides only in small amounts. Formulex will not help you solve this problem in the fish circuit, and its EDTA-chelated iron, stable up to a pH of around 6, would in any case lose its effectiveness in water at 7. The corrections that are safe for fish are targeted: a DTPA chelated iron dosed at around 2 mg per litre, potassium bicarbonate, which raises the pH while also supplying potassium, and a calcium amendment for the calcium. The guide to deficiencies in aquaponics helps you recognise each symptom before you act.

Shake the bottle before each use, then pour the dose into the water, not the other way round, before mixing. In hydroponics, make up a fresh solution each time you empty the tank rather than topping up the old one indefinitely, as its balance shifts as the plants take up nutrients. Between uses, keep the tightly closed bottle in a cool, dry place away from direct light. A 300 ml bottle makes up 60 litres of watering solution at 5 ml per litre, or 30 litres of hydroponic solution at 10 ml per litre, which is enough for several batches of seedlings.

You receive a 300 ml bottle or a 1 L bottle of Formulex, depending on the size chosen, with the manufacturer's label showing the analysis and the doses. The large size suits you if you use a propagator all year round or several seed trays; the small one is enough for a season of seed sowing at home.