yes, this is just a treatment when introducing fish to the system.. salt is one of the few things i'll use if fish are showing signs of stress or infection..
i;ve seen systems that people only add salt when there appears to be trouble with the fish.. 1-3ppt for tonic/treatment.. if a fish shows signs of some kind of infection, i have a "hospital" system i can salt higher.. i only go to 6ppt for yellow perch, i've seen people with tilapia treat with 12ppt - these higher doses will kill plants, thats why i use a hospital tank
most plants will be ok up to 3ppt, but that's when strawberries and cuke's start to suffer/die
just investigate your fish first regarding salt..i've heard/read that catfish won't do very well with salt over 3ppt, so like i said.. do your research