Reef Dosing Calculator

It depends on the gap between your current and target level. A common target is 420 ppm. Measure with a test kit, enter current and target calcium plus your net water volume into the Ca/Alk/Mg tab, and the calculator gives the exact mL of your chosen supplement. Never raise calcium more than 50 ppm in one day — dose half, retest tomorrow, then dose the rest.

Most reef keepers target 7–11 dKH (natural seawater is ~7 dKH). SPS-heavy tanks often run 7–8 dKH; mixed reefs are comfortable at 8–10 dKH. Stability matters more than the exact number — swings of more than 1 dKH per day stress corals more than being at 7.5 vs 9.

1 dKH = 0.357 meq/L = 17.86 ppm as CaCO3. So 8 dKH equals 2.86 meq/L or 142.9 ppm. Use the unit converter in the Product Database tab — it converts dKH, meq/L and ppm CaCO3 in both directions.

Kalkwasser (limewater) is saturated calcium hydroxide solution, pH ~12.5. It adds calcium and alkalinity in the natural balanced ratio (~20 ppm Ca per 1 meq/L alk) while replacing evaporated water — typically dripped slowly overnight via an auto-top-off. One gallon of saturated kalkwasser added to 100 gallons raises calcium by ~9.4 ppm. It maintains levels; it does not efficiently raise low levels. It is caustic: wear gloves and eye protection, never pour the milky slurry into the tank, and never dose it all at once.

Technically yes, but it is the wrong tool for big corrections — you would need roughly 7.5 gallons of saturated solution for a 100-gallon tank, and the pH spike risk is serious. Use a two-part calcium supplement for the correction first, then switch to kalkwasser to maintain the level against daily consumption.

Vodka (ethanol) is a carbon source that feeds bacteria, which consume nitrate and phosphate and are then skimmed out. The classic ramp for 100 gallons net: 0.4 mL/day on days 1–3, 0.8 mL/day on days 4–7, 1.2 mL/day in week 2, increasing ~0.4 mL each week until nitrates fall, then halving to a maintenance dose. A strong protein skimmer is mandatory, and you must test nitrate/phosphate weekly. Stop or reduce if you see bacterial blooms or cyano.

1 mL of 80-proof (40%) vodka is roughly equivalent to 8 mL of 5% distilled white vinegar as a carbon source. Vinegar is gentler on pH-sensitive setups per unit carbon but you dose 8× the volume. The carbon dosing tab converts both directions and builds the ramp schedule for your tank size.

Start dosing when regular water changes can no longer hold your parameters stable between changes — typically when calcium drops 10+ ppm or alkalinity drops 0.5+ dKH per day in a stocked tank. Before that, test weekly for a month and log consumption. Dosing without a consumption history means guessing, and guessing kills corals.

Two-part dosing adds calcium (part A, calcium chloride) and alkalinity (part B, soda ash or baking soda) in balanced amounts — about 20 ppm of calcium for every 1 meq/L (2.8 dKH) of alkalinity — because corals consume them in that ratio. Dose equal volumes daily based on measured consumption, and add magnesium separately when it drifts below 1250 ppm.

Recipe #1 (higher pH): dissolve 2½ cups (~500 g) of calcium chloride dihydrate per gallon for the calcium part, and 1⅛ cups (~594 g) of baking soda per gallon for the alkalinity part. Recipe #2 is half-strength of both. The Product Database tab lists the exact computed strength of each recipe (e.g. Recipe #1 calcium: ~9.5 ppm per mL per gallon). Always use food/pharma-grade chemicals and mix with RO/DI water.

The JDieck calculator (and its mirrors) has been the community standard since the early 2000s and its math is trusted. This tool covers the same core dosing math with a modern interface, adds kalkwasser, vodka/vinegar carbon dosing, nitrate dosing, a daily-dose planner and a product database in one place, and shows every formula so you can verify it. If you trust JDieck's numbers, cross-check ours against it — the chemistry is the same.

Chronically zero nitrate starves corals and invites dinoflagellates. Dissolve food-grade potassium nitrate (KNO3) in RO/DI water and dose to raise nitrate by ~1 ppm per day until you hold 2–5 ppm. The nitrate section computes the exact milligrams of KNO3 for your tank volume. Dose slowly, test daily, and stop if phosphate is also zero — balance both nutrients.

There is no universal mL number because products differ in cell concentration — follow the manufacturer's label as the starting point (commonly ~5 mL per 10 gallons daily for concentrated cultures). The daily planner's 'other supplement' row lets you set any mL-per-gallon rate and scales it to your tank and schedule. Start at half the label dose and watch nutrient levels.

Only when it tests below ~1250 ppm. Magnesium is consumed slowly, so most tanks need it weekly or monthly, not daily. Correct it with magnesium chloride (preferred) or a magnesium chloride/epsom salt blend — epsom salt alone also raises sulfate. Never dose magnesium on the same day as large calcium corrections without retesting.

The usual causes: dosing alkalinity and calcium supplements too close together (they precipitate each other out — dose at least an hour apart, ideally in high flow), a magnesium level below 1250 ppm (low magnesium lets calcium carbonate precipitate spontaneously), or overdosing kalkwasser too fast (pH spike causes a 'snowstorm'). Test magnesium first, space your doses, and dose alkalinity in small amounts through the day.

This is a math tool, not veterinary or professional chemistry advice. Every result is an estimate — always verify with a calibrated test kit, start with half the calculated dose, and never change alkalinity more than 1 dKH or calcium more than 50 ppm in a single day. Kalkwasser is caustic (pH ~12.5): gloves and eye protection are mandatory. When in doubt, ask an experienced reefer or your local fish store before dosing.