Planted tank fertilizer calculator
Dry fertilizers dissolve in the tank water, so the rise in mg/L (ppm) is the grams times the share of the nutrient in the compound, divided by the water volume. Pick a compound and the tank volume, then either enter grams to see the rise, or enter the rise you want to get the grams.
- nitrate (NO3)
- 7.67 mg/L
- potassium (K)
- 4.83 mg/L
Rise from 1 g in 100 liters
| Compound | Adds |
|---|---|
| Potassium nitrate (KNO3) | 6.13 mg/L nitrate (NO3), 3.87 mg/L potassium (K) |
| Monopotassium phosphate (KH2PO4) | 6.98 mg/L phosphate (PO4), 2.87 mg/L potassium (K) |
| Potassium sulfate (K2SO4) | 4.49 mg/L potassium (K) |
| Magnesium sulfate heptahydrate (MgSO4·7H2O, Epsom salt) | 0.99 mg/L magnesium (Mg) |
Notes on the numbers
Nitrate here means NO3, the form most aquarium test kits report in mg/L. Some kits report nitrate-nitrogen (NO3-N) instead, which is about 4.4 times smaller for the same water.
The shares come from atomic masses, for example potassium nitrate is 61.3% nitrate and 38.7% potassium by weight. Fertilizer grades vary a little in purity, so a bag of Epsom salt or potassium sulfate may land a few percent off.
The volume is the water in the tank, which is lower than the size on the tank's label. Use the tank volume calculator if you are unsure. A fertilizer that raises nitrate also adds to what you later remove with water changes.
This page does the arithmetic only. What amounts suit your plants and fish depends on the dosing method you follow, so take the targets from that source.