This guide is written as an operating framework. Exact limits still depend on the organism, system volume, equipment and local rules.
Define the measurement
Specific gravity changes with temperature and instrument calibration. Write down the tool and method used so future readings are comparable.
Mix replacement water separately
Dissolve salt completely, match temperature and confirm the final reading before adding water to livestock. Never sprinkle dry salt directly into an occupied aquarium.
Replace evaporated water with fresh water
Evaporation removes water but leaves salts behind. Top up with suitable fresh water, then use saltwater only for planned water changes or deliberate adjustments.
Make changes in steps
Large salinity changes can stress gills, kidneys and invertebrates. Plan the endpoint and adjust over an appropriate period for the exact species.
Record the actual water volume
Substrate, rock and equipment reduce the water volume below the tank’s advertised size. Dose and mix from measured system volume rather than the label on the glass.
Research and review
This is original AquaNexus writing. It does not reproduce third-party articles, tables, photographs or databases. Species-specific legal and husbandry claims must be checked against current authoritative sources before publication as final guidance.