dGH
GH
What is it
GH, or general hardness, measures dissolved calcium and magnesium. It describes the mineral content animals use for osmoregulation, bone, shell and exoskeleton health.
Why it matters
Fish and invertebrates evolved in waters with different mineral loads. Shrimp need enough minerals for molting, livebearers prefer harder water, while many blackwater species do better in softer water.
Interactions with other parameters
GH is separate from KH: one controls mineral hardness, the other buffering. TDS includes GH plus many other dissolved substances, so it cannot replace a GH test.
Ideal ranges
| Tank type | Min | Max | Unit |
|---|---|---|---|
| Tropical community | 4 | 12 | dGH |
| Planted high-tech | 4 | 8 | dGH |
| Planted low-tech | 4 | 14 | dGH |
| Shrimp tank | 4 | 7 | dGH |
Out of range: what happens
GH that is too low can cause poor shrimp molts, weak snail shells and unstable livestock condition. GH that is too high can stress soft-water fish and reduce breeding success.
Common Myths
- •Hard water is always bad; many species require it to stay healthy.
- •TDS tells you GH exactly; it only gives a broad dissolved-solids reading.
How to measure
Use a liquid GH titration kit and count drops until the color changes. Test source water and tank water, especially after using stones, substrates or remineralizers.
How to adjust
Raise GH with a targeted remineralizer, calcium/magnesium salts or harder source water. Lower it by mixing with RO or deionized water during water changes.
Pro Tips
For shrimp tanks, remineralize RO water to a repeatable GH instead of guessing with tap water.
Watch snail shell edges: pitting or erosion often points to low minerals or low pH.
