Tools
Reef tank calculators
Twelve free calculators for the sums reef keepers do every week. Each one shows its formula in plain words, a worked example, what it cannot do and where its numbers come from. Volumes work in litres, UK gallons or US gallons.
Formulas and sources last checked . How we check
Water and salinity
- Salt mixGrams of salt for a batch, and what your refractometer or hydrometer should read.
- Salinity correctionHow much water to swap, day by day, at a safe pace.
- Water change effectWhat a change, or a run of changes, does to a reading.
- ATO reservoir safetyHow far salinity falls if a stuck pump empties the reservoir.
Dosing and chemistry
Tank, heat, light and power
- Tank volumeLitres from the tank size, and the net water after rock, sand and sump.
- Heater sizeWatts for a UK room, split across heaters so one stuck on is not a disaster.
- Light hours and PARPhotoperiod, ramps, daily light and PAR by coral group.
- Electricity running costWhat the tank costs to run at the current UK price cap.
Livestock
How are these calculators built?
The maths is ours, written out on each page so you can check it by hand. Where a number comes from a brand, such as how much 1 ml of a supplement raises calcium, we name the manual and the date we read it. Where sources disagree, the page says so. Results are worked out in your browser; nothing you type is sent anywhere.