Dosing calculator

From your current parameter reading to the target — how many millilitres of your fertiliser? Works for NO₃, PO₄, K, Fe, Mg, Ca, anything dosed in mg/mL.

Stormy · the watcher

Stormy watches the numbers move. Tell her where you are, where you want to be, and how strong your bottle is — she'll work out the dose.

Tank volume (L)Net water volume, not the rated tank size. Subtract substrate + hardscape if you've measured them.Current (mg/L)Your last test reading for this parameter.Target (mg/L)Where you want the parameter to land after dosing.Product (mg / mL)Concentration from the product label. Aqua Rebell Makro Basic NPK ≈ 10 mg NO₃ / mL.

Fill in all four fields to see the dose.

How this works

Adding x mL of a product carrying mgPerMl mg of the parameter per millilitre raises the concentration in a V-litre tank by x · mgPerMl ÷ V. Solving for x to land at (target − current) gives the dose.

mL = (target − current) × volume (L) ÷ mg per mL

Caveat: this assumes the bottle's labelled concentration is accurate and the tank is well-mixed. Plant uptake during the dose is ignored — fine over short windows, less accurate if you're dosing slowly over hours.

In the app, Manfred logs every dose against the right tank so the next calculation starts from a measured baseline, not a guess.

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