I ask because if there's other stuff there (that is actually taken note of) and hence accounts for the remaining 0.2% specifically, it might not be suitable. But if it's just salt with a bit of impurity (hence 99.8% not 100%), then it's perfectly fine.
I use it if treating freshwater fish for ich. It is NaCl, which is salt, and because it is used for softening water, safe for human consumption, safe for fish.