How many ppm of nitrate does 1 gram of KNO3 add?

KNO3 is 61.33% nitrate by mass (from IUPAC atomic weights), so 1 g adds about 613 mg of nitrate. In 100 L of water that is about 6.1 ppm NO3.

How much potassium is in KH2PO4?

Monopotassium phosphate is 69.79% phosphate (PO4) and 28.73% potassium by mass.

How do I calculate a stock solution dose?

Divide the grams of salt by the bottle volume to get grams per mL, multiply by the mL you dose, then by the mass fraction of the nutrient, and divide by the tank water in liters. The result in mg per liter is ppm.

Entry 03Dry salts

Dry fertilizer salts to ppm

Pick a salt, enter how much goes in, and see the ppm of every nutrient it carries. Works for dosing straight into the tank or from a stock bottle, and in reverse: how much salt for the ppm you want.

Last updatedOct 19, 2026

Mass fractionscomputed from IUPAC atomic weights

Units

Lgal

Salt

Fertilizer salt

Measured in

Amount exampleIn the unit chosen above.

Tank

Water volume example (in liters)After substrate and rock.

Work out your water volume

Stock solution The salt is dissolved in a bottle and I dose from that

Reverse

Target for the first nutrient listed example (parts per million)For example nitrate for KNO₃.

Added to the tank

–

Every nutrient in this dose
Nutrient	Share by mass	Adds

–straight into the tank for the target of

in teaspoons

Mass fractions

How much of each salt is the nutrient you care about follows from its formula. We compute every share from the IUPAC CIAAW standard atomic weights (IUPAC CIAAW¹) rather than copying them from a chart, and show them here so you can check them against any other calculator. The trace mix is different: its shares are the guaranteed minimums from the bag label (NilocG Aquatics²), which match the base CSM's label for every element but boron (Master Plant-Prod³).

Molar mass and composition
Salt	g/mol	Share by mass
KNO₃Potassium nitrate	101.10	NO3 61.33%, N 13.85%, K 38.67%
KH₂PO₄Monopotassium phosphate	136.08	PO4 69.79%, P 22.76%, K 28.73%
K₂SO₄Potassium sulfate	174.25	K 44.88%, SO4 55.12%
MgSO₄·7H₂OMagnesium sulfate heptahydrate (Epsom salt)	246.47	Mg 9.86%, SO4 38.97%
CaSO₄·2H₂OCalcium sulfate dihydrate (gypsum)	172.16	Ca 23.28%, SO4 55.79%
Ca(NO₃)₂·4H₂OCalcium nitrate tetrahydrate	236.15	NO3 52.51%, N 11.86%, Ca 16.97%
KHCO₃Potassium bicarbonate	100.11	K 39.05%, HCO3 60.95%
NaHCO₃Sodium bicarbonate (baking soda)	84.01	Na 27.37%, HCO3 72.63%

Hydrates matter

Epsom salt is magnesium sulfate with seven waters of crystallization, and those waters are 51% of its weight. Calcium nitrate is usually sold as the tetrahydrate and gypsum as the dihydrate. Choose the form on your bag; the anhydrous forms carry more nutrient per gram.

Nitrate or nitrogen, phosphate or phosphorus

Hobby test kits and the EI targets use NO₃ and PO₄. Fertilizer labels in the US report N, P₂O₅ and K₂O. The table above gives both NO₃ and N for nitrate salts and both PO₄ and P for phosphate, so compare like with like.

Teaspoons

A teaspoon of salt is not a fixed weight. In the UK Aquatic Plant Society thread, a member weighed 10 teaspoons and averaged about 6.2 g for KH₂PO₄, 6.5 g for K₂SO₄ and 5.0 g for Epsom salt (UK Aquatic Plant Society forum⁴). The calculator fills those in when you choose a salt. A kitchen scale that reads 0.1 g is the better tool.

Sources for this page

1IUPAC CIAAW: Abridged standard atomic weightsRead Oct 19, 2026
2NilocG Aquatics: Plantex CSM+B guaranteed analysisRead Oct 19, 2026
3Master Plant-Prod: Plantex NutriTrace CSM guaranteed analysisRead Oct 19, 2026
4UK Aquatic Plant Society forum: Teaspoons to grams conversion via chemical densityRead Oct 19, 2026

Every figure above traces to one of these. Formulas are on Methods. Found an error? hello@mosspearl.com