GH Calculator - Tools & Calculators
Units
GH Calculator
Calculate General Hardness (GH) from Calcium (Ca) and Magnesium (Mg) levels.
How do I calculate the general hardness (GH) of my aquarium?
What is general hardness (GH)?
General hardness (GH) measures the total concentration of dissolved calcium and magnesium ions in water. It is one of the most important water parameters for aquarium keeping, affecting fish health, shrimp molting, plant growth, and overall ecosystem stability. GH is commonly measured in degrees (dGH or °dH) or ppm.
How the calculation works
If you know your calcium and magnesium levels in ppm, you can calculate the resulting GH:
GH (dGH) = (Ca ppm ÷ 7.143) + (Mg ppm ÷ 4.348)
Unit conversions
| From | To | Multiply by |
|---|---|---|
| dGH | ppm CaCO₃ | 17.848 |
| ppm CaCO₃ | dGH | 0.056 |
| dGH | mmol/L | 0.1783 |
GH ranges and what they mean
| GH range | Classification | Suitable for |
|---|---|---|
| 0–4 dGH | Very soft | Caridina shrimp, blackwater fish |
| 4–8 dGH | Soft | Most tetras, discus, angelfish, planted tanks |
| 8–12 dGH | Medium | Livebearers, Neocaridina shrimp, community fish |
| 12–18 dGH | Hard | African cichlids, brackish species |
| 18+ dGH | Very hard | Tanganyikan cichlids, specialized setups |
How to adjust GH
- Raise GH: Add GH booster, crushed coral, or limestone. Use remineralizers for RO water.
- Lower GH: Mix with RO or distilled water. Some active substrates also reduce GH.
Tips for managing GH
- Test GH at least monthly, more often when setting up new tanks or after major water changes
- Match GH to your livestock – research the natural habitat of your fish and shrimp
- Stability is more important than perfection – avoid sudden GH swings
- Maintain a healthy Ca:Mg balance (3:1 to 4:1) for optimal plant and invertebrate health