This shock begins performing as soon as you add it to your water and you can bathe after just 20 minutes.Chlorine free shock oxidizer releases used sanitizer and reactives bromine, in particular.  It is considered to be comparable to any part 2 of a two part sanitizer system. Oxy-Clear is a very effective shock when chloramines are high, for example after a party or sports team visits your spa.  Must be used in conjunction with a chlorine or bromine sanitizer.