Hi all,
....By the way Darrel do you know GH of your tap water. Its probably the same as mine.
I do Jose, you can work it out from the figures the water company publishes <
http://www.wessexwater.co.uk/customers/water-quality/waterhardness.aspx?pc=SN13 9AR>.
I have to make the assumption that the magnesium content is negligible, as the water company doesn't provide separate values for magnesium, but this is a fair assumption based on geology (aquifers are Jurassic age limestones).
One millimole of calcium per litre of water corresponds to a hardness of 100 ppm or 5.61 dGH, since the molar mass of calcium carbonate is 100g/mol. (Ca has a RAM of 40, C = 12 and O = 16, CaCO3 = 40 + 12 + 48(16 x 3) = 100).
100g in 1 litre is a molar solution of calcium carbonate (40% Ca), and 0.1g per litre a milli-molar solution.
1 dH is "One degree German" and defined as 10 milligrams of calcium oxide (CaO) per litre of water. The RMM of CaO is 56 (40 + 16) and it is 71.4% Ca.
This is equivalent to 17.85 milligrams of calcium carbonate per litre of water, or 17.85 ppm. (71.4/40 = 1.785 and 10 x 1.785 = 17.85)
2014
Calcium (milligrams per litre) 131.6 (329 x 40%)
Calcium carbonate (milligrams per litre) 329
Degrees German (ºdH)18.424 (18.24 x 17.85 = 329)
These were the corresponding figures in 2009.
Calcium (milligrams per litre) 119 (298 x 40% = 119)
Calcium carbonate (milligrams per litre) 298
Degrees German (ºdH) 16.7 (16.7 x 17.85 = 298)
cheers Darrel