|0 - 3||0 - 50||Soft|
|3 - 6||50 - 100||Moderately Soft|
|6 - 12||100 - 200||Slightly Hard|
|12 - 18||200 - 300||Moderately hard|
|18 - 25||300 - 450||Hard|
|Over 25||Over 450||Very Hard|
GH is the unit used to tell us the General hardness of the water. Or how much Calcium and/or Magnesium are dissolved in the water.
Only Calcium and Magnesium are measured and not the overall amount of dissolved solids. The GH level isn't really of importance unless you want to breed your fish or unless it is extremely high.
Excessive amounts of Calcium in the water will affect the fish's fertility and it will also make the outer membrane of the eggs tougher so that fewer eggs will be fertile and those that are fertile may fail to hatch. There are not very many fish that prefer really hard water other than some African Cichlids (from Lake Tanganyika) and some Livebearers.
Lowering the GH.
Raising the GH.