Aquarium Equip Dr. Marine Glass Saltwater Hydrometer Thermometer Reef Soft Coral Ensures proper gravity of aquarium water. Easy to use. Ensures all water has the same salinity within aquarium Green indicators are ideal range of water temperature and specific gravity for most salt water / marine aquariums. Measure both Temperature and Specific Gravity of the water. SIZE19.2CM(7.5"). Glass Hydrometer; Measures Celsius and Fahrenheit