True, goldfish especially any of the fancier breeds can only tolerate that stuff for short periods of time. Usually meant for parasite control or treatment. Excellent for anchorworm. However, my experience has been that adding SOME salt especially when breeding or with incubation works in favor of higher hatchings and lower mortality. Again, I can't prove that it's the salt, there's too many variables at play. But I believe that some is better than none...as long as you plant appropriately for whatever concentration you use. I know my peach trees, orange tree, and apples like a LITTLE salt when we move them....seems to eliviate leaf drop and such. But I have no measurements for this. For those I measure by the handfull....I know not very scientific.