Yep, what Dave said.....I used aquarium salt regularly in my tanks for 3 years with no apparent ill effects......until the beginning of this year that is.
I only started using salt when I first got into this hobby, because my brother in law told me to...(he has a few tanks)...figured he knew what he was talking about.
I was told by folks here that it wasn't a good idea, but I had never experienced any ill effects so I continued. (I figured the day I stopped I'd have some kind of major catastrophy or other....lol....Murphy lives in my back pocket)
Anyway, I noticed at one point that one of my angels was not acting right...not eating and hanging in the corner. I hadn't added anything new to the tank, was doing regular routine twice weekly gravel vac/water changes...in other words, there was no reason for it to be sick that I could see. I stopped adding salt to the change water and did some major water changes in that tank and the angel came around and has been doing fine ever since.
I saw that as the first indication of trouble because of the salt...that angel is a 'weaker' fish....not sickly or anything, just not as robust as my other angel and if something was going to go wrong in my tank, that would be the first fish to show signs..and he was. I haven't used aquarium salt since...and no..I didn't have any major catastrophies from the change......lol....