General Hardness
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°GH - General Hardness[edit]
General, total or permanent hardness is a measure of the overall concentration of calcium, magnesium and other ions. It's measured in degrees, with one degree equal to about 17.9mg/l (17.86mg/l). The degree symbol is often replaced with a "d" (i.e. 6dGH or just 6dH). The harder the water, the higher the GH number.
- Some countries measure GH in ppm (like the USA), others use the German unit dH.
- Some countries use 'GCH' (General Carbonate Hardness) instead of 'GH'.
- Some retailers (ADA) use TH abreviation (Total Hardness)
| Degrees | Parts Per Million | Description |
|---|---|---|
| 0 - 4 dH | 0 - 70 ppm | wet |
| 4 - 8 dH | 70 - 140 ppm | soft |
| 8 - 12 dH | 140 - 210 ppm | medium |
| 12 - 18 dH | 210 - 320 ppm | firm |
| 18 - 30 dH | 320 - 530 ppm | hard |
| Higher | > 530ppm | solid |
Raising GH[edit]
If you live in an area with low GH water you may need to add chemicals to increase the GH level to a level suitable for your aquatic animals.
- Calcium carbonate (CaCO3) is a typical and cheap material to do this. You can find it as Coral sand, coral pieces, sea shells, Cuttle-bone pieces, etc. It is also sold in gardening shops as 'Lime' usually in a powder form. It will however raise KH as well as GH. Which is probably a good thing if you live in a soft water area.
- Magnesium sulphate (MgSO4) or more commoningly known as Epsom salt. This will raise GH without altering KH. Used in a ratio of 1:3 with CaSO4 (Calcium sulphate) (1 part MgSO4 to 3 parts CaSO4) to make your own GH mix for a freshwater aquarium.
Links[edit]
- See The Krib for more on this.
- Hardness: A Term with Many Meanings
