Free Tool

Reef Dosing Calculator

Brand-agnostic dosing for alkalinity, calcium, magnesium, nitrate and phosphate. Enter your own concentrations, build DIY two-part stocks, track consumption, and get doser-pump schedules — with every formula and source shown. Free, no login, your data stays on your device.

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Reef dosing calculator showing an alkalinity dose result with safety warnings and the math shown

One Calculator for Your Whole Reef Chemistry Workflow

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Dose Any Additive

Alk, Ca, Mg, NO₃ and PO₄ in both directions: current → target, or "what does 10 ml actually do?" Works with DIY chemicals and any brand via custom concentrations.

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DIY Two-Part & Balling Builder

Grams of salt + water → per-ml potency, fed straight back into the dose calculator. Randy's Recipes #1 and #2 built in, with solubility warnings.

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Consumption → Standing Dose

Two tests a few days apart become your daily consumption rate and the standing daily dose that holds parameters steady — plus a doser-pump schedule.

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Safety Built In

Auto dose-splitting for corrections over 1.4 dKH/day, Ca+Alk precipitation warnings, kalkwasser pH-spike alerts, and net-volume math so you never dose against gross volume.

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Show the Math

Every result has an expander with the formula, constants, and source — grounded in Randy Holmes-Farley's published reef chemistry articles.

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No Login, Offline, Private

Everything runs in your browser and saves to your device. No account, no upload, no subscription. Works at the tank with no signal.

Built to Replace the Calculator the Hobby Lost

Dose Calculator — Both Directions, Any Brand

Pick a parameter, pick an additive (or enter your own concentration the way labels state it), and get the exact ml or grams. Reverse mode tells you what a given dose will change. Corrections that exceed safe daily limits are automatically split across days.

  • Alkalinity in dKH, meq/L or ppm CaCO₃ (1 meq/L = 2.8 dKH = 50 ppm)
  • DIY chemicals built in: soda ash, baking soda, calcium chloride, magnesium chloride/Epsom blend, KNO₃, NaNO₃, KH₂PO₄, TSP
  • Custom additive entry: "X ml in Y gallons raises Z" — stored locally
  • BRS-style dose splitting over 1.4 dKH/day; gentle 0.5 dKH/day guidance
  • Never-dose-Ca-and-Alk-together and low-Mg-first warnings
Dose calculator showing dose result with split-over-days warning

DIY Stock Builder + Consumption Tracking

Build two-part and Balling-style stock solutions from dry salts and feed the resulting potency straight into the doser. Then measure your tank's daily consumption from two dated tests and get the standing dose and pump schedule that hold it steady.

  • Randy's Ca stock (500 g CaCl₂·2H₂O/gal ≈ 36,000 ppm) and balanced alk recipes
  • Solubility warnings (why Recipe #2 needs two gallons)
  • Consumption = (test 1 − test 2) ÷ days + existing dosing
  • ml/day → ml-per-dose × doses/day with evenly spaced times
  • Minimum-pump-volume warnings for tiny doses
DIY stock solution builder showing per-ml potency result

Water Change, Salt Mix, Kalkwasser & Tank Volume

The adjacent math every reefer needs: dilution effects of water changes, how big a change reaches a target, salt mix amounts, salinity correction, kalkwasser dosing from RHF constants, and net water volume with rock/sand displacement.

  • Water change: C = C₁(1−f) + C₂·f, single or repeated changes
  • Salt mix grams for any volume and salinity target
  • Kalkwasser: saturated = 40.8 meq/L, ~808 ppm Ca, pH 12.54 (RHF)
  • Net volume = gross × fill % × (1 − displacement %) + sump
  • Unit converter: dKH ↔ meq/L ↔ ppm CaCO₃, SG ↔ ppt ↔ mS/cm, gal ↔ L
Water change and salt mix calculators

Reef Dosing FAQ

About 0.019 g of soda ash (Na₂CO₃) per liter per dKH — roughly 1.9 g per 100 L to raise 1 dKH. Baking soda needs ~1.6× more (0.030 g/L/dKH) and lowers pH slightly instead of raising it. The calculator does this for any tank volume and also builds liquid stock solutions.
Enter your current and target values and pick the DIY stock (or your brand with a custom concentration). The math is simple: dose = desired raise × tank volume ÷ potency, where potency is how much 1 ml raises 1 liter. Every result shows the formula and constants used.
Common guidance: keep corrections gentle at ~0.5 dKH per day, and never exceed ~1.4 dKH per day (BRS guidance — larger corrections should be split over consecutive days). The calculator splits oversized corrections automatically.
Concentrated calcium and carbonate/bicarbonate react on contact and precipitate as calcium carbonate — the classic "snowstorm". Dose them at least 20–30 minutes apart into high flow, and keep doser schedules for the two parts offset.
Test, wait 2–3 days without changing anything, test again: consumption/day = (first − second) ÷ days, plus whatever you were already dosing. The Consumption tab computes it and converts it into a standing daily dose and doser-pump schedule.
Saturated limewater is ~40.8 meq/L (114 dKH) with ~808 ppm calcium at pH 12.54. Adding 1.25% of tank volume raises alkalinity ~0.5 meq/L (1.4 dKH). Because of the high pH, drip it slowly — most reefers limit kalk to evaporation top-off volume.
Yes — KNO₃, NaNO₃, KH₂PO₄ and trisodium phosphate are built in with molecular-weight-exact math (KNO₃ is 61.3% nitrate; a 10 g/L stock is ~6,100 ppm NO₃). Raise nutrients slowly and retest before dosing again.
No proprietary concentrations are shipped — vendors like Triton don't publish them. Instead, add a custom additive: enter the potency from the label ("X ml in Y gallons raises Z") or from your own measurements. It's saved locally and works in every tab.
1 meq/L = 2.8 dKH = 50 ppm CaCO₃ (Randy Holmes-Farley). So 8 dKH = 2.86 meq/L = 143 ppm CaCO₃. The Unit Converter tab also handles salinity (SG 1.0264 @ 25 °C = 35 ppt = 53 mS/cm) and gallons ↔ liters.
Rock, sand and equipment displace typically 10–25% of a tank's gross volume. Dosing calculated against gross volume systematically overdoses — dangerous in nanos. The Tank Volume tab estimates net volume and saves it to your profile.
No. Everything runs in your browser; your tank profile and custom additives are saved in local storage on your device. No account, no upload, no tracking of your tank data.
The constants are from Randy Holmes-Farley's published reef chemistry articles (Reefkeeping magazine, Reef2Reef) and straight molecular-weight arithmetic. Every calculation has a "Show the math & sources" expander. Doses are estimates — always test before and after.

Stop Guessing Your Doses

Any additive, all the math shown. Free. No signup.

Open Reef Dosing Calculator