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What one dose does
PARAMETER
1 ml / 100 L
Magnesium
+0.4694 ppm
To raise magnesium by 50 ppm in 100 L: 107 ml.
How it’s used
1,285 g (7 1/4 cups) MgCl2·6H2O + 124 g (1/2 cup) MgSO4·7H2O, start half-full and top to 1 US gal. Stoichiometric 43,815 mg/L Mg, 12,767 mg/L SO4; BRS calculator example (100 gal, +30 ppm -> 241.9 ml) implies 46,946 mg/L. perMlEffects use calculator basis.
Cautions
• Part 3 cannot be premixed with the calcium or alkalinity parts (sulfate + Ca -> CaSO4; Mg + carbonate -> precipitate). Some CaSO4 haze in the jug is expected; shake before dosing.
• Ratio choice: sulfate-rich blends (RHF Part 3A, 5:3 by cups = ~1.4:1 by weight; BRS 2-part version ~2.8:1 by weight) are meant to be used WITH a CaCl2-based two-part, whose chloride load needs extra sulfate; a stand-alone Mg supplement for corrections is better at ~10:1 MgCl2:MgSO4 by weight (RHF, relayed; BRS general mix 1285 g:124 g).
• Raise Mg no more than ~100 ppm/day; wait 5 days off-dosing before setting a maintenance dose (BRS).
• Cup measures are approximate; weigh where possible.