Aquarium Hydrometers and Salinity Measurement

Hydrometers measure specific gravity or salinity in marine and reef aquaria. Accurate salinity control is essential for the health of marine fish, invertebrates and corals, so choosing the right tool matters.

Types and accuracy

Glass floating hydrometers are simple and inexpensive but can be influenced by temperature and surface tension. Digital refractometers provide more precise readings and are easier to calibrate, while optical devices deliver fast, repeatable results. Consider the required accuracy for your system—reef tanks often need tighter control than fish‑only setups.

Use and maintenance tips

• Calibrate devices regularly and follow temperature correction guidelines.
• Rinse instruments with fresh water after use to prevent salt buildup.
• Keep a spare testing tool for cross‑checking important measurements.

Look for deals on test equipment or refurbished refractometers if budget is a concern, but prioritise accuracy and calibration capability. Consistent salinity monitoring helps prevent stress and supports stable aquarium ecosystems.