Bromine
—When Bromine is used as a disinfectant, a residual of 1 ppm shall be maintained for a pool with a pH below 7.8
—2 ppm for pH 7.8 or higher
http://tbn0.google.com/images?q=tbn:q5YnHHNiMabPTM:http://www.camlab.co.uk/siteimages/periodic_icons/bromine.gif http://tbn0.google.com/images?q=tbn:M52hJ8MFNAZkuM:http://content.answers.com/main/content/wp/en-commons/thumb/3/3b/200px-Bromine-trifluoride-3D-vdW.png http://tbn0.google.com/images?q=tbn:QLJwApY15_1AeM:http://www.aqua-pool-warehouse.com/ig/Others/Chemicals-bromine_1.othr.jpg http://tbn0.google.com/images?q=tbn:PJLPzYqLMm5KuM:http://spapartsnet.com/mc/ap/40115.jpg http://tbn0.google.com/images?q=tbn:vcgtdbnlxHLsKM:http://www.iscapoolcare.co.uk/webupload/ISCA/SMALL/bromine-granules.jpg