ACS is what i have. it only allows half the impurities that USP does. it is very pure. i believe BP is equivalent to USP. you can take that for life.
a nice little 100ml brown liquor bottle will do nicely. or get a kilo and do it in a one liter bottle.
i gave the exact results you should get with real KI. if all the crystals dissolve much sooner or if it doesnt fill at least half the container when you put it in, then i would question strength and purity. certainly cheap enough to try.