Reef Tank Top-Off Mistakes That Cause Salinity Drift
Avoid the most common auto top-off and manual top-off errors that destabilize salinity and stress reef livestock.
Salinity drift is one of the most common hidden stressors in reef aquariums. Corals may look “off” for weeks before obvious symptoms appear. The good news: most drift comes from a few preventable top-off mistakes.
1) Topping off with saltwater instead of fresh RO/DI
Evaporation removes freshwater, not salt. Always replace evaporation with fresh RO/DI water. Save saltwater for water changes only.
2) Letting ATO sensors foul or stick
Salt creep and film buildup can cause overfill or underfill. Clean sensors regularly and test fail-safes monthly.
3) Using an oversized top-off reservoir without safeguards
A massive reservoir can dump too much water if a float sticks. Use dosing limits, dual sensors, and alarms.
4) Ignoring seasonal evaporation changes
Winter heating and summer humidity alter evaporation rates. Recheck salinity at least weekly and after HVAC or fan changes.
5) Skipping manual verification
Even with a controller, verify with a calibrated refractometer. Track values in the ReefBay app so trends are obvious before livestock suffers.
Helpful gear and livestock links
Compare marketplace options for ato, heater, and fan. If stress already affected livestock, browse hardy recovery-friendly options like zoa and toadstool.
Quick checklist
- Top off with fresh RO/DI only
- Clean ATO sensors weekly
- Use fail-safes and max-run limits
- Calibrate refractometer often
- Log salinity trend weekly
Consistent salinity is one of the biggest upgrades you can make for long-term reef stability.
