Kent Marine poly-ox is not potassium permanganate it is H2MnO4 that acts like potassium permanganate (KMnO4). Kordon Permoxyn is 3.8% potassium permanganate KMnO4. If you decide to go this route hydrogen peroxide is the antidote.
If I were going to try this method I would first set up a test tank and test what strength is needed to kill the vermetid snails. Then I would test it with a few pieces of different expendable coral frags to see how they react.
Some information on KMnO4 can be found at
http://www.discusforums.com/forum/ar...p/t-20752.html