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Hardness, Calcium, Magnesium

Because I have been adding Calcium and Magnesium without really knowing how
quickly they are (or aren't) being taken up by the plants, I bought a HACH
hardness and calcium test kit, which provides magnesium by difference.  I
would appreciate some help in interepreting the results:

Hardness = 140 mg/l.
Calcium = 80 mg/l.
By difference, Magnesium = 60 mg/l.

I believe these numbers are all in terms of CaCO3.  Am I correct in then
multiplying the Calcium reading by 40/100 or 0.4 to obtain the Ca++
concentration and the Magnesium reading by 24/100 or 0.24 to obtain the Mg++
concentration?  This would mean:

Ca++ = 32 mg/l
Mg++ = 14 mg/l

Firstly, if these calculations are not correct, what should they be?.

Secondly, I have found rather wide ranges of recommended levels for these
two nutrients in the archives, but there seems to be some agreement on a
ratio of Ca to Mg of 2:1 or 3:1, with a Ca range of 15-75 mg/l and an Mg
range of 5-25 mg/l.  Are these ratios and ranges still the recommended
values?  If not, what should I be aiming at?

Thanks in advance for your corrections and advice.

John T. Fitch
Tel/Fax (617) 494-4882
E-mail: JTFitch at FitchFamily_com
Web Page: www.fitchfamily.com