A one-time correction to bring alkalinity, calcium, or magnesium up to target, with the dose split over days so you never raise it too fast. For a daily maintenance plan built from your test history, see the Pro two-part dosing planner.
How it's calculated
Dry chemicals use stoichiometry: sodium bicarbonate (84.01 g/mol, 1 meq per mmol) needs 30.0 mg/L per dKH; soda ash (105.99 g/mol, 2 meq per mmol) 18.9 mg/L per dKH; calcium chloride dihydrate 3.668 mg per mg of calcium; magnesium chloride hexahydrate 8.365 mg and magnesium sulfate heptahydrate 10.14 mg per mg of magnesium. Liquid Recipe 1 two-part is about 1 mL per US gallon for 1.4 dKH or 10 ppm calcium. Corrections are split so no day exceeds 1.4 dKH, 50 ppm calcium, or 100 ppm magnesium. Test again before each day's dose.
Magnesium is usually dosed as a 7:1 to 10:1 chloride-to-sulfate mix by weight; dosing only sulfate for months raises sulfate. Related: how to raise alkalinity, calcium, magnesium, and the unit converter.
FAQ
How much can I raise alkalinity in one day? Keep it to about 1.4 dKH per day or less; many reefers prefer 1 dKH. This calculator splits bigger corrections over several days so no day goes over the limit. Calcium up to about 50 ppm a day and magnesium about 100 ppm a day are the usual guidelines.
How much baking soda raises alkalinity by 1 dKH? About 30 mg of sodium bicarbonate per liter, or 0.11 g per US gallon. For 100 gallons that's about 11.4 g per dKH.
Should I dose alkalinity and calcium together? Not at the same moment or the same spot. Add them a few hours apart into high flow so they don't precipitate as calcium carbonate.
Sources
- Randy Holmes-Farley, "Solving Calcium and Alkalinity Problems" and the "Recipe 1" two-part (Reefkeeping Magazine): 1 mL per US gallon raises alkalinity about 1.4 dKH and calcium about 10 ppm
- Randy Holmes-Farley, "Chemistry and the Aquarium: What is Alkalinity?" (Advanced Aquarist, 2002): 1 meq/L = 2.8 dKH = 50.04 mg/L as CaCO₃