Procedure
1 Put on protective gloves and goggles.
2 Rinse the hydrometer a few times with the water to be sampled. Make sure that the needle swings freely and no salt deposits are built up on the inside.
3 Holding the hydrometer at a slight angle with the opening along the top, gently lower it into the water.
Allow the water to slowly flow into the hydrometer and push out all the air, leaving as few bubbles as possible. Air bubbles will affect your reading.
4 Holding the hydrometer steady, carefully remove any remaining bubbles along the needle with a pencil, so that the needle swings freely.
5 Allow the needle to stop moving, then read the amount of salt in your water in parts per thousand (ppt).
6 Rinse the hydrometer with clean water a few times between readings. Let it soak for a couple of hours in vinegar to remove all salt deposits before storing. Do not disassemble the hydrometer.
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Testing for Salinity with a Hydrometer