Saltwater Water Change Calculator
Plug in your tank's net water volume and a target percentage — the calculator tells you how many gallons of fresh saltwater to mix up. Net volume is the actual water in your system, after subtracting rock and sand displacement.
Not sure of your net volume? Use the tank volume calculator first. For the cadence and technique, see our water changes guide.
Net volume = display + sump − rock and sand displacement.
Routine: 10% weekly or 20% biweekly. Restorative: 25–30%.
Mix this much new saltwater
- US gallons
- 5
- Liters (approx.)
- 18.9
Mix the new saltwater in a dedicated container — never directly in the display tank. Match temperature and salinity before adding.