Aquarium Plant Fertilizer Dosing Calculator
Calculate precise fertilizer doses for your planted aquarium based on tank size, plant density, and lighting level.
How Aquarium Plant Fertilizer Dosing Works
Aquatic plants require three categories of nutrients: macronutrients (nitrogen, phosphorus, potassium), micronutrients (iron, manganese, boron, zinc), and carbon (typically supplied via CO2 injection). The Estimative Index (EI) dosing method provides a reliable baseline for planted tanks.
Key Dosing Formulas
Potassium Nitrate (KNO3) dose in grams:
Dose = (Target_ppm × Tank_Liters) / 180,000
For a typical target of 20 ppm NO3 in a 200-liter tank: Dose = (20 × 200) / 180,000 = 0.022 g per dose
Potassium Phosphate (KH2PO4) dose:
Dose = (Target_ppm × Tank_Liters) / 220,000
Micronutrient (trace) dose scales linearly with tank volume and is adjusted by a plant density multiplier:
- Low density: 0.5×
- Medium density: 1.0×
- High density: 1.5×
Lighting also affects uptake. High light (above 50 PAR at substrate) increases nutrient demand by roughly 50% compared to low light (below 20 PAR).
Worked Example
A 300-liter tank with high plant density and medium lighting:
- KNO3: (20 × 300) / 180,000 × 1.5 = 0.050 g per dose
- KH2PO4: (3 × 300) / 220,000 × 1.5 = 0.006 g per dose
- Trace mix: 0.05 mL per liter × 300 × 1.5 = 22.5 mL per week
EI Dosing Reference Table
| Tank Size (L) | KNO3 (g/week) | KH2PO4 (g/week) | Trace (mL/week) |
|---|---|---|---|
| 100 | 3.2 | 0.5 | 10 |
| 200 | 6.4 | 1.0 | 20 |
| 400 | 12.8 | 2.0 | 40 |
Dose macros and micros on alternating days (Mon/Wed/Fri and Tue/Thu/Sat), with a 50% water change on Sunday to reset nutrient levels and prevent accumulation.