Randy Holmes-Farley Part 3B (Epsom-only magnesium)
magnesium
MgSO4·7H2O
Manufacturer data
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What one dose does
PARAMETER
1 ml / 100 L
Magnesium
+0.4702 ppm
To raise magnesium by 50 ppm in 100 L: 106 ml.
How it’s used
64 oz (~8 cups, 1814 g) Epsom to 1 US gal -> ~47,000 ppm Mg and ~187,000 ppm sulfate (published). Check: 1814 x 0.0986/3.785 = 47,266 mg/L Mg; x 0.3897/3.785 = 186,801 mg/L SO4. Add 610 ml each time one gallon of Part 1 AND one gallon of Part 2 have been used (Recipe #1); 305 ml for Recipe #2. Alternative to the preferred 3A blend.
Cautions
• Sulfate-overload caution: each ppm of Mg from Epsom adds 3.95 ppm sulfate. Raising Mg 100 ppm with Epsom alone adds ~395 ppm sulfate (natural seawater ~2,700 ppm). Use Epsom alone only for small corrections; RHF's model shows Epsom-only Part 3 pushing sulfate to ~3,840 ppm in a year.
• For large corrections use mostly MgCl2·6H2O (BRS general mix ~10:1 chloride:sulfate by weight).