Fertigation Recipe & A/B Tanks, Done Right

Fertigation is delivering dissolved fertilizer through the irrigation system, usually drip. A concentrated stock solution is injected into the line at a set ratio so every plant gets nutrients with its water. It is efficient and precise, but it only works if the salts are weighed correctly, stay in solution, and never mix in a way that precipitates and clogs emitters — which is exactly what this tool checks.

It starts from a target nutrient solution in ppm of each element and meets them in a fixed order: calcium from calcium nitrate, phosphorus from mono-potassium phosphate, magnesium and sulphur from magnesium sulphate, the remaining potassium from potassium nitrate, and any remaining nitrogen from urea. Grams of salt per litre of final solution = ppm ÷ (10 × percent element), so each target is converted directly to a salt mass.

Because calcium must never share a concentrated tank with sulphate or phosphate. In concentrate, calcium reacts with sulphate to form insoluble gypsum (calcium sulphate) and with phosphate to form calcium phosphate — both precipitate as a sludge that clogs filters and emitters. So calcium nitrate goes in tank A, sulphates and phosphates go in tank B, and neutral salts like nitrates and urea can go in either. The tool assigns each salt and flags any clash.

It is the dilution, written 1:R — one part stock concentrate to R parts water in the line. At 1:100, one litre of stock makes 100 litres of final irrigation solution, so the concentrate must be 100 times stronger than the target. The tool uses your ratio to size the stock tank concentration and then checks it against each salt's solubility limit.

Each salt has a cold-water solubility limit in grams per litre, listed in the table on this page. The concentrate must hold R times the per-litre dose, so the tool computes the stock-tank concentration (g/L) for each salt and flags any that exceed the solubility limit. If a salt is over-limit, lower the injection ratio (more dilute concentrate), split into more tanks, or use a more soluble source.

Electrical conductivity (EC) measures the total dissolved salts in the final solution, in dS/m, and is the everyday check on whether the feed is too strong or too weak. The tool estimates it from the total fed ppm using the USDA conversion 1 dS/m ≈ 640 mg/L. Most greenhouse feeds run around 1.5–3.0 dS/m; well above that risks salt stress, which the verdict flags.

Fertilizer bags often quote N-P2O5-K2O (oxide basis), but plants take up P and K as elements. This tool's salt table is on the elemental N-P-K-Ca-Mg-S basis, matching how nutrient-solution targets are written in ppm. That avoids the oxide-to-element conversion errors that throw off many hand-built recipes.

Yes. The chemistry is identical — a target ppm solution, A/B tank separation and an injection ratio apply to recirculating hydroponics, run-to-waste systems and open-field drip alike. The generic Hoagland-like recipe is a good starting point for soilless systems; the crop-stage recipes suit greenhouse and field fertigation.

It means a calcium salt and a sulphate or phosphate salt have been assigned to the same tank, which will precipitate. With the standard A/B scheme the tool keeps them apart, so an incompatible flag points to a forced constraint. The fix is to move the offending salt to the correct tank, or to use a different nitrogen or potassium source that does not carry the conflicting ion.

The tool reports kilograms of each salt to charge the stock tank for the final volume that tank's concentrate will make. That is the grams-per-litre-of-final-solution dose times the litres of final solution the tank serves, converted to kg. Weigh each salt separately, dissolve fully, and never tip dry salts together.

Dissolve into a part-filled, slightly warm tank with the agitator running, adding the most soluble and slowest-reacting salts first, then top up to volume. Keep calcium in tank A and sulphates/phosphates in tank B as the tool assigns. Add any acid last and slowly. The tool tells you which tank each salt belongs in so you never combine the conflicting ones.

Yes — source water already carries calcium, magnesium, sulphate and bicarbonate that add to your targets, and bicarbonate may need acid to neutralise. This tool sizes the fertilizer salts from the target ppm; for hard or alkaline water, run a water analysis and subtract the water's contribution before setting your targets, and add acid separately.

It is a solid, deterministic recipe from published salt analyses and solubility data and your targets. Real practice depends on water quality, temperature, the exact product grade and injector accuracy, so treat it as a strong starting point. Mix a batch, measure the EC and pH, and fine-tune. Always verify tank separation and solubility before scaling up.