Magnesium (Mg) Calculator - Tools & Calculators
Magnesium (Mg) Calculator
Estimate Magnesium (Mg) level from General Hardness (GH) and Calcium (Ca).
How do I calculate magnesium in my aquarium water?
Why is magnesium important for planted tanks?
Magnesium (Mg) is the central atom in chlorophyll – without it, plants cannot photosynthesize effectively. It is also a key component of general hardness (GH) alongside calcium. Magnesium deficiency causes yellowing between leaf veins (interveinal chlorosis), especially in older leaves. Many aquarium fertilizers overlook magnesium, making it a common limiting nutrient.
How the calculation works
Since GH is the sum of calcium and magnesium hardness, if you know your GH and calcium level, you can derive magnesium:
Ideal magnesium levels
| Tank type | Mg (ppm) |
|---|---|
| Planted tank (general) | 5–15 ppm |
| High-tech planted tank | 10–20 ppm |
| Shrimp tank | 5–10 ppm |
Signs of magnesium deficiency
- Yellowing between leaf veins while veins stay green (interveinal chlorosis)
- Symptoms appear first on older leaves (Mg is mobile in plants)
- Overall pale or light green coloration
- Stunted growth in severe cases
How to raise magnesium levels
- Magnesium sulfate (Epsom salt): Readily available, 1 g per 50 L raises Mg by ~2 ppm
- Magnesium chloride: Alternative if sulfur is not desired
- GH boosters: Commercial products add balanced Ca and Mg
Keep the Ca:Mg ratio in mind
Most experts recommend a Ca:Mg ratio of 3:1 to 4:1. If you raise GH with a product that only adds calcium, magnesium may become deficient. Always check both values when adjusting water hardness.