Quick answer
Evaporation removes water but leaves salt behind, so top off with fresh purified water. Saltwater is used for water changes, not routine evaporation replacement.
What to check first
- Measure salinity with a calibrated instrument
- Mark the normal water level
- Check auto-top-off sensors
- Consider daily evaporation changes
Write down the test results, recent maintenance, new livestock, feeding changes and equipment faults. A short timeline prevents repeated guesses and makes patterns easier to see.
A practical action plan
- 1. Top off slowly with fresh RO/DI waterRecord what changes and retest before making another major adjustment.
- 2. Calibrate the refractometer or conductivity meterRecord what changes and retest before making another major adjustment.
- 3. Correct large errors graduallyRecord what changes and retest before making another major adjustment.
- 4. Keep the return chamber level stableRecord what changes and retest before making another major adjustment.
What to avoid
Do not top off with mixed saltwater or make abrupt salinity corrections around invertebrates.
When it is urgent
A large salinity error with distressed livestock should be corrected carefully with expert guidance.
How to prevent it next time
Use stable routines: quarantine additions, test before and after major changes, maintain backup aeration, keep equipment accessible, and record enough detail to compare today with the aquarium’s normal baseline. Prevention is usually cheaper and safer than emergency correction.
Research and review
This is original AquaNexus writing prepared for practical aquarium use. The husbandry framework was checked against authoritative veterinary, safety, scientific or specialist references.
Test rather than guess and make changes at a pace the livestock can tolerate. This guide does not replace aquatic veterinary advice. Follow product labels and local electrical-safety requirements.