How often should I calibrate my reef refractometer?

Calibrate your reef refractometer at least once every month as part of routine maintenance. You should also recalibrate before mixing a new batch of saltwater, after any accidental drop, after major room-temperature swings, and any time a salinity reading does not match coral or fish behavior. For the most accurate baseline, use a proper 35 ppt calibration solution instead of relying on RO/DI water alone. After calibration, test both your display tank and your freshly mixed saltwater before water changes or large top-off adjustments. Stable salinity protects coral tissue, improves polyp extension, and helps fish avoid osmotic stress. Keep your refractometer lens clean, store it dry, and recheck calibration if readings drift unexpectedly. This simple habit takes only a minute, but it prevents many avoidable stability issues in beginner and advanced reef systems.