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
| °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 |
