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If you're raising saltwater fish, you'll want to measure the specific gravity and salinity of your aquarium on a weekly basis to maintain an ideal environment. Normal salinity in a marine aquarium is between 0.03 percent and 0.05 percent. Normal specific gravity is between 1.02 and 1.024. An ocean hydrometer is the easiest way to take both readings.
Using the Hydrometer
Rinse your hydrometer with pure water before filling it to make sure it is clean. Immerse the hydrometer in your tank, allowing it to fill completely. Remove it and set it on a level surface. Tap the side of the hydrometer lightly with a pencil or plastic spoon to dislodge bubbles. Observe the needle as it moves to the proper reading for the specific gravity and salinity.
Be sure to rinse your hydrometer with pure water again, and dry thoroughly, before putting it away. Otherwise, mineral deposits can affect the next reading. Saline deposits may accumulate on the needle after a few uses. Soak the hydrometer in a bowl of water deep enough to completely cover it; add a tablespoon of vinegar to the water.
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