Aquarium Water Hardness
In a nutshell, the higher is a concentration of metal ions in aquarium water the harder water is.
These metals are sodium, calcium, magnesium, iron, zinc and other, but
mostly the focus is on magnesium (Mg) and calcium (Ca)
Keep in mind that there are several types of water hardness degree. So reading some article specify which degree author means. Most freequently used is German degree (dGH).
water hardness conversion
Table 1
Given unit of water hardness
|
Coefficient to convert into German degree
|
 French
degree |
0.5603 |
 British
degree |
0.7987 |
 American
degree |
0.0560 |
`
Types of water hardness
There are three types of water hardnss, that are important for aquarium:
Temporary (carbonate) hardness (dKH). It's the hardness derived mainly from carbonate and bicarbonate ions
AKA alkalinity hardness. Can be reduced by boiling:
Ca(HCO3)2
―
t→ CaCO3↓ + CO2
+ H2O
Mg(HCO3)2
―
t→ MgCO3↓ + CO2
+ H2O
Permanent hardness (dNKH)
Can NOT be reduced by boiling.
This if concentration of sulphates, nitrates, chlorides etc.
For example CaCl2, MgSO4 etc.
General hardness (dGH)
General hardness is a sum of two prior ones:
dGH = dKH + dNKH
(note that sometimes other symbols are used by authors of web articles, for example dH or GH instead of dGH; but the maening is the same).
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