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What one dose does
PARAMETER
1 ml / 100 L
Calcium
+0.37 ppm
To raise calcium by 20 ppm in 100 L: 54.1 ml.
How it’s used
BRS pouch = 498.95 g (about 2.5 cups) to 1 US gal. Stoichiometric if pure dihydrate: 35,934 mg/L Ca. BRS calculator worked example (100 gal, +10 ppm -> 102.3 ml) implies 37,003 mg/L, i.e., the same ~37,000 ppm basis as Randy Recipe #1; perMlEffects use the calculator basis.
Cautions
• Never dose the calcium part and the alkalinity part at the same spot/time or premix them; CaCO3 precipitates.
• Keep calcium increases <=50 ppm/day for large corrections (BRS guidance).
• Two-part dosing adds NaCl as a by-product (CaCl2 + Na2CO3 -> CaCO3 + 2 NaCl); monitor salinity and do periodic water changes.
• Ice-melt products vary in purity and hydration; unknown brands are untested for heavy metals.
• Hydration state changes Ca per gram: anhydrous 36.1% Ca, dihydrate 27.3%, hexahydrate 18.3%.