Reef Calculator
Dosing, salinity, salt mix, tank volume — every calculation a reefer needs in one place.
Reef Chemistry Calculator
Precision dosing for calcium, alkalinity & magnesium
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Tank volume (used for the daily-rise math) is taken from the shared Tank Volume field at the top.
Daily delivery from kalkwasser top-off
Enter your daily evaporation above to see how much Ca and alk your top-off delivers.
Recipe
Add — g of Ca(OH)₂ (calcium hydroxide / pickling lime / hydrated lime) to — gal RO/DI.
- Stir vigorously for 1–2 minutes until milky.
- Cap tightly — atmospheric CO₂ converts Ca(OH)₂ to insoluble CaCO₃, ruining the batch over 24–48 h.
- Let settle 12–24 h. The clear top supernatant is your dosing fluid.
- Decant gently — leave the white sediment in the bottle.
- Use within 1–2 weeks. A fresh white film on top means CO₂ contamination — restart.
About kalkwasser. Kalk has a pH near 12 — drip slowly into a high-flow area and never dose more than your evaporation replacement rate. Saturated kalkwasser is caustic; wear gloves and eye protection when mixing. Verify Ca and alk weekly with a calibrated test kit and adjust strength if your tank's demand drifts.
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Note: Conversions use a linear approximation valid for the reef aquarium range (1.018–1.030 SG) at 25 °C / 77 °F reference temperature. Always verify with a calibrated refractometer or conductivity meter.
Using an older 60 °F-calibrated hydrometer?
Many older swing-arm hydrometers are calibrated to 60 °F (15.6 °C). At typical reef tank temperatures (75–80 °F / 24–27 °C), the same actual salinity will read lower on a 60 °F hydrometer than on a 25 °C-referenced device. As a rough rule of thumb, add about 0.0035–0.0040 to a 60 °F hydrometer reading to estimate the equivalent 25 °C SG — but a refractometer is far more reliable.
Salt Required
Why does my brand differ in practice?
Salt mix density and moisture content varies between brands and even between batches of the same brand. Manufacturers' grams-per-gallon figures are a starting point — not a guarantee. Always verify the final salinity with a calibrated refractometer before using the water in your tank.
Standard rectangle tank. Enter outside-glass dimensions for the gross figure.
Enter L × W × water height (not chamber height) for each baffled section.
Always test after dosing • Ca 380–450 ppm • Alk 7–12 dKH • Mg 1250–1350 ppm • Dose gradually — never spike parameters
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