Please help with calcs: GH/CaCl2/MgSo4 - The Planted Tank Forum
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post #1 of 2 (permalink) Old 04-03-2005, 01:19 PM Thread Starter
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Please help with calcs: GH/CaCl2/MgSo4


I could use some help from gurus double checking my calcs.

My well water reads 0 GH and my goal in the calcs is to use CaCl2 (anhydrous - Prestone driveway heat, MW 111) and MgSO4.7H20 (Walmart epsom salts, MW 246.3) to increase 100 liters of water by 5 GH with a 4:1 ratio of Ca++ to Mg++.

Since it would take me all day to type in my actual calculations, I have instead typed in the answers I got and hope someone out there who is a water chemistry guru can help me double check my thinking and numbers.

By definition, 1 degree GH is 10 mg per liter CaO. I calculate equivalents to this to be:

7.143 ppm Ca++ = 7.143 mg/L Ca++
0.179 mM Ca++/L
0.179 mEq Ca++ (or total divalent cation)/L

So to increase 5 degrees would be 0.895 mEq cation/L, of which I would want 4/5 calcium and 1/5 magnesium, so

0.716 mEq/L Ca++ and 0.179 mEq/L Mg++

I calculate these to need:

7.9 g CaCl2 per 100 liters to increase by 4 GH, and
4.4 g MgSo4.7H20 per 100 liters to increase by 1 GH

Are these calcs correct? Are any of the assumptions incorrect? Thank you for you feedback.

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post #2 of 2 (permalink) Old 04-03-2005, 03:14 PM
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Ca++ has a valency of 2 so 1dH = 0,358mEq/L Ca++

The calculations are correct
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