Ray-JrMALL Sea Hydrometer Saltwater Test Meter for Fish Tank Water Salinity Specific Gravity Test Aquarium Automatic Accurate Readable Hydrometer Salt Water S. The color of the point in the center is random. Quickly, easily, and accurately measure your marine aquarium's salt level and specific gravity with Instant Ocean Hydrometer Higher Accuracy than other slat water and gravity tester.: 0.001. Feature: Accurate, durable, and easy to read sea water salt water hydrometer. Small and waterproof. No sensor wire needed. Unique Design: This product is designed with an automatic level function, can automatically identify the level to avoid errors.