The Coral Sea Hydrometer is the perfect tool for marine aquarium keepers to maintain a healthy saltwater reef aquarium. Accurate and easy to use, this hydrometer provides precise readings of salinity and salt content, ensuring the ideal environment for your marine aquarium. Its durable construction and portable, easy-to-read design, the Coral Sea Hydrometer is suitable for any experience level marine aquarist. Measuring the salt content of water (specific gravity), the Coral Sea Hydrometer helps maintain optimal conditions for your fish, invertebrates, and live corals and ensures new water matches the salinity required for your tank. Easy-to-use, simply dip it into water, and the accurate readings are displayed instantly. With its clear markings and easy-to-read scale, measuring salinity has never been easier. The durable construction of the hydrometer ensures its longevity and reliability for long-term use in your saltwater reef aquarium. Ideal for use in water temperatures ranging from 68°F to 85°F, readings are temperature-corrected & accurate to +/- 0. 001. specific gravity units ranges from 1. 014 - 1. 030 with a safe zone of 1.020-1.024. The outside range of scale indicates salinity ppt, ranges from 20 -40 ppt, safe zone is 27-32.