Why should salinity or specific gravity be measured?

Natural sea water is the most ideal condition for all marine species but is difficult to replicate. One of the closest ways to create such an environment is to determine the water density which essentially is the concentration of minerals in the water. The major element in sea water is salt; the more salt, the higher the density. Density is traditionally measured using a float hydrometer which gives a unit of measurement called specific gravity.

Most aquarist handbooks use this unit of measurement to recommend the amount of salt to be added into a tank. As the hydrometer is calibrated at 15°C, a correlation table must be used to get the correct reading. A simple pointer-hydrometer does not even have a table to make correlations, thus the measurement is highly inaccurate. This is one of the reasons why so many fail to keep a marine aquarium.

Modern technology has advanced with new method of measuring salinity via the conductivity method which allows user to obtain reading of salinity in gram per litre. This is usually represented by ppt (parts-per-thousand). The best feature about this method is that readings are automatically compensated despite measuring in differing temperatures. Reading is accurate up to 2ppt or 0.002sg.