My understanding is that you really need a minimum of 1 tsp per gallon for treatment and 2-3 tsp per gal. I don't know about dosage when using it as a tonic for nitrite stress, I've never used salt in that particular scenario. With ich, there is some suspicion that it can survive low levels of salt, So I would take any chances with it. If you check the useful links sticky there are a couple of good articles on both ICH and salt in the thread. and as alwaays a wealth of info elsewhere, There are many credible sources, and many questionableand it's hard to sort them out.
Lastly in case someone misunderstood. I don't want to give the wrong impression so I should clarify that I am willing to spend whatever it takes to keep my fish happy as long as they are in my care. Every article that I have ever seen that said table salt was a no-no has been in some way or another related to someone who sold aquarium salt for profit. I prefer to save dimes when I can because it equates to more and bigger fish tanks as well as more trips to the LFS for stuff I just gotta have
) . 