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Aquarium Dosing Calculator

Planted-tank and shrimp keepers often dose a dry compound (for example potassium nitrate or magnesium sulfate) and need to know how many grams raise one ion by a certain ppm (mg/L). This calculator does the arithmetic from the compound's chemical formula. It also converts the result into a stock solution so you can dose with a syringe instead of a tiny scoop.

Units Tank net water volume Not sure? Use the volume calculator first. Compound you are dosing Fractions are the mass share of the ion in the pure compound, from standard atomic masses. Ion fraction for "Other" (0 to 1, e.g. 0.25 means 25% of the powder's mass is the ion) Purity of your product (%) Check your product's label. Leave 100 if it is a pure grade or unknown. Wanted increase of the ion (ppm = mg/L) Optional stock solution: grams of powder dissolved in how many mL of water in total

Enter your tank volume, the compound and the ppm increase, then press Calculate.

How it is calculated

Water in liters: US gallons × 3.78541.
Grams of powder: ppm × liters ÷ 1000 ÷ ion fraction ÷ purity fraction.
Stock solution: concentration = grams ÷ mL. The mL to add equals grams needed ÷ concentration.

Reference: ion fractions used

Compound	Ion	Share of mass
KNO₃	NO₃	61.3%
KH₂PO₄	PO₄	69.8%
K₂SO₄	K	44.9%
MgSO₄·7H₂O	Mg	9.9%
CaCl₂·2H₂O	Ca	27.3%

Limits: the tool only does arithmetic. It does not know your current water values, your livestock or your plants, and it does not tell you what to target or how often to dose. Measure your water with a test kit, follow a reliable specialist source for your animals and plants, and change values slowly. A stock solution of a hydrated salt depends on which form you own, so check the formula on the package. Real tanks lose nutrients to plants, algae and water changes, so results are estimates.