Sodium is not salt - it is one of a number of elements that can bond to make a salt. Metals in groups 1 and 2 on the periodic table readily will bond with gases in groups 16 and 17 to make salts (other elements can as well). Sodium is found on food nutritional facts because table salt is NaCl (sodium chloride). Now that's not saying there aren't elements or compounds in your aquarium that the sodium could bond to making salt, but sodium by itself does not make salt nor does it raise salinity.
