don't worry about the anticaking additive. PP is for the "advanced" fish keeper as you can literally dissolve fish and cause an explosion if mixed with the wrong stuff. It is a very effective treatment though and cheap.
http://forum.simplydiscus.com/showthread.php?70066-Using-Potassium-Permanganate-aka-PP
http://forum.simplydiscus.com/showthread.php?70066-Using-Potassium-Permanganate-aka-PP