Just some info I picked up doing some research:
"There are a lot of misconceptions about the various salts available for aquarium use. One such misunderstanding is that non-iodized salt is not the same as aquarium salt nor are either of these the same as marine salt. Table Salt is nothing more than Sodium Chloride (NaCl). It comes in iodized and non-iodized forms. Aquarium Salt is very similar to table salt inasmuch as it is made of Sodium Chloride (NaCl) as well; however, it lacks anti-caking ingredients and iodine. Epsom Salt is Magnesium Sulfate (MgSO4). Marine Salt, on the other hand, is no simple recipe. Below is a listing of its constituents:
Chlorine, Cl 19,500
Sodium, Na 10,770
Magnesium, Mg 1,290
Sulphur, S 905
Calcium, Ca 412
Potassium, K 380
Bromine, Br 67
Carbon, C 28
Nitrogen, N 11.5
Strontium, Sr 8
Oxygen, O 6
Boron, B 4.4
Silicon, Si 2
Fluorine, F 1.3
Argon, Ar 0.43
Lithium, Li 0.18
Rubidium, Rb 0.12
Phosphorus, P 0.06
Iodine, I 0.06
Barium, Ba 0.02
Molybdenium, Mo 0.01
Arsenic, As 0.0037
Uranium, U 0.0032
Vanadium, V 0.0025
Titanium, Ti 0.001
Zinc, Zn 0.0005
Nickel, Ni 0.00048
Aluminium, Al 0.0004
Cesium, Cs 0.0004
Chromium, Cr 0.0003
Antimony, Sb 0.00024
Krypton, Kr 0.0002
Selenium, Se 0.0002
Neon, Ne 0.00012
Manganese, Mn 0.0001
Cadmium, Cd 0.0001
Copper, Cu 0.0001
Tungsten, W 0.0001
Iron, Fe 0.000055
Xenon, Xe 0.00005
Zirconium, Zr 0.00003
Bismuth, Bi 0.00002
Niobium, Nb 0.00001
Thallium, Tl 0.00001
Thorium, Th 0.00001
Hafnium, Hf 7 x 10-6
Helium, He 6.8 x 10-6
Beryllium, Be 5.6 x 10-6
Germanium, Ge 5 x 10-6
Gold, Au 4 x 10-6
Rhenium, Re 4 x 10-6
Cobalt, Co 3 x 10-6
Lanthanum, La 3 x 10-6
Neodymium, Nd 3 x 10-6
Lead, Pb 2 x 10-6
Silver, Ag 2 x 10-6
Tantalum, Ta 2 x 10-6
Gallium, Ga 2 x 10-6
Yttrium, Y 1.3 x 10-6
Mercury, Hg 1 x 10-6
Cerium, Ce 1 x 10-6
Dysprosium, Dy 9 x 10-7
Erbium, Er 8 x 10-7
Ytterbium, Yb 8 x 10-7
Gadolinium, Gd 7 x 10-7
Praseodymium, Pr 6 x 10-7
Scandium, Sc 6 x 10-7
Tin, Sn 6 x 10-7
Holmium, Ho 2 x 10-7
Lutetium, Lu 2 x 10-7
Thulium, Tm 2 x 10-7
Indium, In 1 x 10-7
Trebium, Tb 1 x 10-7
Palladium, Pd 5 x 10-8
Samarium, Sm 5 x 10-8
Tellurium, Te 1 x 10-8
Europium, Eu 1 x 10-8
Radium, Ra 7 x 10-11
Protactinium, Pa 5 x 10-11
Radon, Rn 6 x 10-16
I hope this has clarified for you what constitutes the various salts available to you and other aquatic hobbyists."