There will always be debates on what type of salt can be used for the aquarium. In short, salt is salt (Table, Kosher, Water Softener, Aquarium...it's all basically sodium chloride or NaCl).
To dispel the myths... many argue that iodine in table salt is toxic to fish. Believe it or not, some fish can suffer from goiter and the trace amounts of iodine may actually prove beneficial for your fish. Other than that, the trace levels of iodine found in regular table salt (like Morton's) is so small that at treatment levels it is no where near toxic levels.
Second myth... It contains anti-caking agents like yellow prussiate of soda that is toxic to fish. The quantity of ant-caking agents used for food grade salt is (once again) so small that your fish would suffer from exposure to high salinity before it would suffer from toxicity due to the anti-caking agents.
That being said, I am also a firm believer that salt should only be used for treatment purposes only. Nature has already sorted out which fish are fresh, brackish, and marine...who are we to change it? It serves no purpose in an already healthy tank.
I use Instant Ocean salt mix. It is for saltwater tanks. I use it for my cichlid tank and to treat my Rhom's heater burn. I also have a saltwater tank so I always have it on hand. It is 100% phosphate free.
It is also the best dissolving salt mix out there.
My Dad used table salt for years to treat cuts and abrasions on his freshwater fish, never a problem.