0 to 4 dH 0 to 70 ppm very soft
4 to 8 dH 70 to 125 ppm soft
8 to 12 dH 125 to 200 ppm medium hard
12 to 18 dH 200 to 300 ppm hard
18 to 30 dH 300 to 500 ppm very hard
over 30 dH over 500 ppm extremely hard

2014-12-30T20:35Z[GMT]