I wouldn't poo poo the idea. Pool salt doesn't contain contaminants as you've mentioned in your post. This is true because pool salt must be edible to humans I.e "table grade" in order to be safely used in pools. I haven't used pool salt for an aquarium as I am freshwater only but If the question of contaminants is the only issue preventing a pool salted tank you are misinformed.
I have used pool salt for 10+ years with zero issues, I have even used it with everything from discus to American cichlids to flowerhorn.
You are absolutely correct, pool salt has to be TABLE GRADE and fit for human consumption since we will probably swallow it while swimming it cannot have contamination.....
Save your dollars and buy pool salt!
