Magnesium
Mg2+Definition
Magnesium (Mg2+) is the trace element that prevents calcium and bicarbonate from precipitating out of solution. Without sufficient Mg, dosing Ca and Alk fails.
Practical use
Reef target: 1300-1400 ppm. Test monthly; supplement with magnesium chloride + sulfate (8:1 mix mimics natural seawater). Low Mg is the most common cause of "I dose Ca but it stays low."
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