What's the deal with aquarium salt?

So, as I've been reading some posts on this forum, I have heard a lot of different opinions on aquarium salt. One said that aquarium salt stresses fish. So now I am completely confused!

I have used aquarium salt for as long as I have had both of my aquariums. On the box it says it provides nutrients and helps their coloring. None of my fish are stressed, so why do some people say that it stresses them? What's your opinion on aquarium salt?
First of all, it depends on the fish. Danios are extremely hardy little fish, and can survive an extremely wide range of water parameters. Bettas can do relatively okay in a wide range of water parameters. On the other hand, some fish do very poorly with salt in their water. Any scaleless fish, for example, suffers from the addition of salt.
Second, it depends on what water you are starting with. Some people have extremely soft water. Adding salt lessens the osmotic stress on the fish's cells, if the fish are generally hard-water fish. In the case of soft-water fish, or if the water source is already hard, salt can end up being harmful.
Third, stress in fish is not necessarily a visible phenomena, especially when you don't have both stressed and unstressed fish to compare each other to. For example, many people keep goldfish in little bowls and say "oh, they seem happy," but when they are convinced to move their fish into a filtered tank, they are amazed at the brighter colors and the increased activity.
ok then what's the difference between aquarium salt and stuff like instant ocean?
The marine salts are made to replicate seawater. They've got trace bits of various minerals in them. These minerals are needed by ocean fish, and particularly by ocean inverts like corals.
Not sure what the aquarium (medicinal) salt has in it, but I know that it's missing these things.
I'm gunna have to agree that the salts are not the same.. for a fish such as a columbian shark u can't used aquarium salt to make the waters brackish and then marine.. instant ocean (or other brands) is required for these changes.

also have to agree that it does depend on the type of fish that u are adding salt with. not all scaleless fish react poorly to salts tho... as I mentioned above.. columbian sharks require a change in the salinity of the water.. if they don't get it they could very well die from lethal skin conditions. but many scaleless can be weakened from the salts.. really does depend...
Aquarium salt is an irritant to freshwater fish. It really isn't needed for them and can cause a number of problems including over-production of slime coating and dehydration. They want you to buy the box, so they don't say that on it. A liquid vitamin like Vita-Chem or even certain foods, like cyclo-peeze, do MUCH more for nutrients and color.
Here is a break down of what's in the different "salts"

I am not advocating using any of these products just showing what's in each of them and their differences.
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