Reef: Aquarium Chemistry Calc

Saltwater chemistry that pairs calcium and alkalinity the way the chemistry works. Magnesium-first guidance, daily-rise caps, dose history. No subscription.

Reef is a chemistry calculator for saltwater reef-keepers. Log a test, get a dose. No accounts, no subscription, no ads.

The dose engine pairs calcium and alkalinity the way the chemistry actually works. When you dose calcium with a two-part product, you have to dose alkalinity alongside it in matched volumes — otherwise the ratio drifts and you end up chasing one parameter while the other crashes. Reef sizes both doses together against your tested gap, your tank volume, and the specific concentration of the product you use (BRS Pharma, Aquaforest, ESV B-ionic, Tropic Marin All-For-Reef, or a custom product).

Magnesium gets its own treatment. If your Mg sits below 1280 ppm, Reef tells you to fix that first — calcium and alkalinity won't stay in range without it. This is standard reef-keeping practice, but most calculators bury it.

Doses are capped to safe daily rises (about 20 ppm Ca, 1.4 dKH Alk) so you don't crash the tank reaching for a target in a single day. Larger gaps get split across multiple days, with the schedule laid out for dosing pumps.

Test history lives on a chart so you can see your alkalinity drift over weeks instead of guessing from memory. Dose history sits beside it so you can see what worked.

Everything stays on your device. Reef has no internet connection, no analytics, no accounts. Buy it once.

Built for mixed-reef, SPS, and LPS tanks.