GH
GH — General Hardness
What is it?
GH (Gesamthärte) measures the total concentration of calcium (Ca²⁺) and magnesium (Mg²⁺) ions. It is the "total hardness" of the water.
Units: °dGH (1 °dGH = 17.9 ppm CaCO₃)
Why It Matters
- Fish: Many species have specific hardness requirements for osmoregulation
- Plants: They need Ca and Mg to grow
- Corals/Invertebrates: Calcium needed for the shell/skeleton
- Shrimp: Very sensitive; low GH → molting problems, death
Recommended Values
| Type | Recommended GH |
|---|---|
| Amazonian / Discus | 1–4 °dGH |
| General Tropical Freshwater | 5–15 °dGH |
| African cichlids | 10–20 °dGH |
| Neocaridina Shrimp | 6–10 °dGH |
| Caridina Shrimp | 4–6 °dGH |
| Marine | 1250–1350 ppm Ca (approx. 70 °dGH equiv.) |
How to Modify GH
Increase GH:
- Calcium chloride (CaCl₂): increases Ca
- Magnesium sulfate (MgSO₄, Epsom salt): increases Mg
- Specific remineralizers (Salty Shrimp GH+, Seachem Equilibrium)
- Hard tap water
Lower GH:
- Reverse osmosis