Specific gravity

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Specific Gravity (sg) is the ratio of the density of a liquid against the density of pure water.

Typically used in the measurement of salt content in brackish, marine or reef aquarium. A hydrometer, or a refractometer are typical devices used to measure sg.

Although sg is a good way of measuring salt content, it can be influenced by other factors like dissolved organic matter in planted aquaria as well as any medications used.

Effects on s.g. by Temperature[edit]

°C/°F sg with salinity at 30.6ppt
7°C (44.6°F) 1.025
13°C (55.4°F) 1.024
18°C (64.4°F) 1.023
22°C (71.6°F) 1.022
25°C (77°F) 1.021
28°C (82.4°F) 1.020
31°C (87.8°F) 1.019
34°C (93.2°F) 1.018
37°C (98.6°F) 1.017