When sodium bromide is used, the bromide is oxidized by chlorine to hypobromous acid (HOBr), which is effective at killing algae. Bromine does not combine with cyanuric acid (CyA) so is not moderated in its strength so is most useful when CyA levels are too high to raise the Free Chlorine (FC) level high enough to kill algae effectively. The presence of bromide cancels out cyanuric acid’s ability to protect chlorine from being broken down by sunlight.
What do I do when I'm done with the Brominated water and I want to go back to Chlorinated water?