Calcium
Ca²⁺. Reef target: 380–450 ppm (most stable reefs sit at 420–440).
Used by coral for skeletal calcium carbonate. Consumed in tandem with alkalinity at 1:1 molar ratio (20 ppm Ca per 1 meq/L alk, or about 7.15 ppm Ca per dKH).
Recommended
Affiliate linksTest kit + DIY two-part chemical.
Salifert Calcium test kitPairs with the alk kit for two-part dosing tracking.View on Amazon →BRS Pharma Calcium Chloride (Ca component)CaCl₂·2H₂O (dihydrate) flake for two-part dosing. Matches Randy's recipe math.View on Amazon →
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