O2 Safe Shock is a non-chlorine shock which yields more than 12% active oxygen (3 times more oxygen than persulfate compounds). O2 Safe Shock can be used as an acid wash pretreatment, making tough copper stains much easier to remove. O2 Safe Shock is not recommended for chlorinated pools, but ideal for biguanide, ozone, and ionization systems. O2 Safe Shock should only be used with Stain Solution #2 - The Copper and Scale Stuff.