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3 fluid ounces of 8.25% bleach in 425 gallons is 4.8 ppm FC but is only 2.1 ppm bromine so added to your initial 1 ppm bromine that gets you to around 3 ppm bromine, not to the 5-6 if that's what you were shooting for. Are you sure you are looking at the bromine ppm on your test kit and not the chlorine ppm? If looking at chlorine then 1+4.8 is close to the 6 you were looking for, but again only if this was all ppm chlorine.Anyway, adding chlorine after a soak to make more bromine is really still a bromine sanitation system at its core since chlorine reacts with the bromide bank to make bromine rather quickly so you don't actually have chlorine for very long in the spa and certainly don't have any when you are soaking. Also note that if one has an ozonator, then it makes bromine from the bromide bank as well, and it also oxidizes bather waste directly too.