Fertigation Stock Tank & Stock & Diluted Strength

A stock tank holds a concentrated fertiliser solution that is injected into the irrigation line at a fixed ratio rather than dosed straight into the whole water supply. Because only a small amount is injected per unit of irrigation water, a manageable tank can fertilise a large area, and the injector controls exactly how strong the water reaching the crop is.

Stock concentration = fertiliser amount ÷ tank volume. For example 5 kg of fertiliser dissolved in a 100-litre tank gives 50 g/L of stock solution. That is the strength of the concentrate sitting in the tank, before it is diluted by injection into the irrigation water.

The injector ratio is how much irrigation water each unit of stock solution is mixed into — written like 1:100, meaning one part stock to one hundred parts water. Venturi injectors, dosing pumps and proportional injectors all set this ratio; it determines how strong the diluted solution that actually reaches the crop will be.

Diluted concentration = stock concentration ÷ injector ratio. So 50 g/L of stock at a 1:100 injector ratio reaches the crop at 0.5 g/L. The calculator works out both the stock concentration in the tank and this diluted concentration in the drip line from your fertiliser, tank volume and ratio.

Injecting a concentrate lets a small tank treat a large irrigation flow, keeps the fertiliser easy to mix and store, and lets you change the injector ratio to fine-tune crop feeding without remixing. It also means you can run the same stock at different strengths simply by adjusting the injector.

It depends on your injector and target feed strength; common venturi and dosing-pump ratios run from about 1:50 to 1:200. Set the ratio so the diluted concentration matches the crop's recommended feed (often a fraction of a gram of nutrient per litre), then keep the stock concentration within the fertiliser's solubility limit.

Be careful — some fertilisers react and precipitate when combined (for example calcium with phosphates or sulphates), clogging the system. Many growers run separate stock tanks (often A and B tanks) and only combine them once diluted in the line. Check compatibility before mixing, and stay below solubility limits.

Enter the fertiliser amount and tank volume in your preferred units (for example kilograms and litres) and the injector ratio; the tool returns the stock concentration and the diluted concentration so you can confirm both the tank strength and what the crop actually receives. Pair it with the Fertigation and Hydroponic Nutrient calculators for full mixes.

The arithmetic is exact for the values entered, but real dosing depends on accurate injector calibration, full dissolution of the fertiliser, water quality and temperature. Calibrate the injector, check the actual ratio with a measured drawdown, and verify strength with an EC meter for reliable feeding.