Important before you start
These figures are a rough starting point, not an exact dose for your specific product. They're based on industry-typical rates for standard liquid fertilizers (roughly 10 ml/25 gal/week for low-tech up to roughly 25 ml/25 gal/week for high-tech). Actual concentration varies significantly by manufacturer and product — always cross-check against the dosing recommendation on your fertilizer bottle, and when in doubt, start with half the calculated amount.
Target values for a well-fertilized planted tank
| Parameter | Target range |
|---|---|
| Nitrate (NO3) | 10–20 ppm |
| Phosphate (PO4) | 0.1–0.4 ppm |
| Potassium (K) | 10–15 ppm |
| Iron (Fe) | 0.05–0.2 ppm |
| Magnesium (Mg) | > 10 ppm |
You can check these values with your water test or our Water Parameter Advisor.
Finding the dose that's actually right for you
The most reliable way to find your true nutrient demand is to measure at the start of the week and again right before your next water change — the difference is your weekly consumption. Divide that by 7 for a daily dose if you'd rather fertilize daily instead of weekly (usually gives more even plant growth).
Signs of too little fertilizer: slow growth, small leaves, pale colors, chlorosis (yellowish new leaves). Signs of too much: increased algae growth, especially staghorn/beard algae with excess iron.