Salinity Drift: Check the Water and the Instrument

Water level and salinity are connected, but they are not the same measurement. A normal-looking waterline can hide an instrument problem or a top-off system doing the wrong thing.

Follow the water movement

Evaporation removes water while leaving most dissolved salts behind. Routine evaporation replacement therefore normally uses suitable fresh water, not newly mixed saltwater. A water change replaces removed aquarium water with prepared saltwater; these are different jobs.

Check the measurement

Follow the instrument maker's calibration and temperature guidance. Keep the measurement surface clean and use an appropriate standard. Specific gravity, salinity and their displayed units should not be mixed casually when comparing readings from different tools.

Inspect the top-off system

• Confirm the reservoir contains the intended water.
• Check that the sensor and delivery mechanism actually operate.
• Look for unusual evaporation, leaks or saltwater removal.
• Record the date and result instead of relying on water level alone.

Avoid an abrupt response

If the reading is unexpected, verify it and work out the cause before making a large change. Appropriate correction depends on the current value, the animals and the system; this post does not prescribe a universal adjustment.

Join the discussion

How do you check salinity?

Sources and further reading

• Randy Holmes-Farley: preparing and measuring saltwater