Thank you for the information Jay, but I am actually looking for how much of an increase in GH would X amount of MgSO4.7H2O have on Y volume of water.
I've done the math and wonder if someone could test it out. Add 1 teaspoon MgSO4.7H2O (~5.4 gram) to 10 gallon (~38 liter) of water and see if the GH will increase by 3 degrees. Scale down/up if you don't have a spare 10 gallon tank around.
Isn't one german degree = 17.9 ppm? 17.9 ppm= 17.9 mg/liter. For gallons you would need 17.9 x 3.77 = 67.5 milligrams of Mg to raise one gallon 1 deg GH. Epsom salts are 9.9% Mg. So you would need 67.5/.099 = 681 mg of Epsom salts to raise 1 gallon of water 1 deg GH. Thats .7 gram Epsom salts to raise 1 gallon 1 deg GH.
OK, thanks for the correction. My little instruction booklet that came with the AP test kit says that GH is a measure of the total Mg++, and Ca++ positive ions in the water. So I was just including the ions, not the entire CaCO3 as the basis of the measurement. I guess I was taking the instructions too literally.