Plastic dosing pipettes, 3 or 5 ml, sold in packs

The pipette also has its place in small-volume soilless growing. A jar using the Kratky method, a seedling tray on a wick or an indoor planter holds only one or two litres of solution, and every millilitre of concentrated fertiliser counts. The CALMAG AGENT soft water corrector is dosed at 0.1 to 0.5 ml per litre: for a 5 L watering can, the dose falls between 0.5 and 2.5 ml, which the 3 ml pipette measures to within 0.2 ml. The fruiting booster for fruiting vegetables is dosed at 1 ml per litre, never more, which is 3 ml for a small 3 L watering can. Both products feed crops grown in soil or in hydroponics and never go into the fish water. Measure the water first, then add each component separately with its own pipette, mixing between additions, and check the pH last. For larger volumes, a precision scale or a graduated syringe takes over, the pipette remaining the tool for fine adjustments.

In aquaponics, the plants' water is also the fish's water, and an addition that is too abrupt is felt first in the tank. New Mexico State University recommends a pH of 6.8 to 7.0 as a compromise between fish, nitrifying bacteria and plants, and advises alternating calcium hydroxide and potassium hydroxide to raise it towards 7, since nitrification gradually lowers it. These bases are best diluted in a bucket of water from the system before being poured in, and the syringe is then used to draw up the exact dose of solution. This way you keep corrections slow, leaving time to check the water between two additions. The article on pH regulation in aquaponics sets out the thresholds to observe.

Iron is often lacking in aquaponics, because fish feed supplies little of it. The FAO manual advises maintaining 1 to 2 mg/L of chelated iron, and the same university recommends adding DTPA chelated iron at 2 mg/L every three weeks. For a small volume, a stock solution is easy to prepare: 1 g of 11% DTPA chelated iron contains 110 mg of iron, and dissolved in 110 ml of water, it supplies 1 mg per millilitre. One millilitre then brings half a litre of water to 2 mg/L, and 4 ml is enough for a 2-litre seedling tray. For a system of several hundred litres, weigh the powder on the scale instead.

A complete hydroponic fertiliser, however, never goes into the fish water. It belongs in pots and seedlings raised before they enter the system, or in a decoupled installation, where a separate growing loop receives the fish water without returning it to the pond and where plant nutrition can be supplemented. The same pipettes then dose the fertiliser for the growing loop, without a drop reaching the fish tank.

Finally, keep separate pipettes for the tank water and for the fertilisers: the one that draws the sample for a test must never have touched a concentrate, otherwise the reading will be skewed. Rinse it in the tank water just before sampling, so that clear water left in the barrel does not dilute the sample, and always sample from the same spot. For the exact volume of the test, follow the dropper or syringe supplied with the test. The aquaponics water test pack tracks pH, ammonium, nitrites, nitrates and carbonate hardness after each correction.