I do know that MPS (potassium monopersulfate) will cause interferance in testing chlorine levels. It might also cause interference in testing the biguinide oxidizer levels. Not really sure. Your best bet is to use chlorine (and a lot of it) to oxidize the biguinide. (And have the pool store test your chlorine levels...not biguinide levels and H2O2 levels....not important once you start the conversion.) The conversion will be complete when the pool clears (after going through some disgusting color changes) and the chlorine is holding.