Major brands of artificial sea salts are now so well compounded that they support even the most delicate types of marine life. Perhaps the worst thing about artificial sea salts is that they are usually made up with city tap water. As when using tap water for a freshwater tank, these compounds must be removed before a sea salt mix is added. Although artificial sea salts are far more convenient and pollution free than most natural seawater, the freshwater source used to mix up the sea salts must be processed if necessary. Passing the water through an activated carbon filter before adding the salt mix is always a good idea.
Salinity is a measure of how much salt is in the water.
Seawater usually has about 28 to 35 parts of salt per 1000 parts of water. As the salt content of water increases, the weight and density of the water also increase. Increased density makes an object float higher. Thus, changes in density can be easily measured as specific gravity with a hydrometer, which floats in the water. The specific gravity of pure water is 1.0000.