ReefMath
Free
Reef chemistry, solved

Exact doses for your reef

Pick your additive, enter your test numbers, get the mL. Safe daily limits are built in and unsafe corrections split themselves across days.

Don't know your water volume? Estimate it
Dose
0 mL
Always confirm with your test kit before and after dosing. Never exceed the daily limit.

More reef tools

Quick answers for the rest of tank day.

Salt mix: how much for new saltwater
Rule of thumb: 1 ppt needs about 1 g per liter. Brands vary a little; check your salt's label and confirm with a refractometer.
Salinity too high: how much water to replace
Replace that much tank water with fresh RO/DI, in steps, retesting as you go.
Water change effect on nitrate or phosphate
Each change removes a fraction of what is left, so repeated small changes beat one big one for stability.
Alkalinity unit converter
Type in any field; the other two follow. 1 meq/L = 2.8 dKH = 50 ppm CaCO3.

Every calculator

One page per additive, with the potency, a worked example and safe limits.

Alkalinity
BRS Soda Ash BRS Sodium Bicarbonate ESV B-Ionic Part 1 Red Sea Foundation B Tropic Marin All-For-Reef Seachem Reef Fusion 2 Kalkwasser limewater Kalk pump rate (mL/hr) DIY Soda Ash (Randy R1)
Calcium
BRS Calcium Chloride ESV B-Ionic Part 2 Red Sea Foundation A Seachem Reef Fusion 1 DIY Calcium Chloride (R1)
Magnesium
BRS Magnesium Mix Red Sea Foundation C DIY Magnesium (R3A)
Guides
Ideal alkalinity (dKH) Ideal calcium (ppm) Ideal magnesium (ppm) How to raise alkalinity How to raise calcium How to raise magnesium Alkalinity too high

Track it. Coming to iOS.

Log every test, see your consumption rate, and let ReefMath recommend tomorrow's dose. Reminders for testing, dosing and water changes. The calculator stays free forever.

Try the web tracker↗