THERE ARE MULITPLE REASONS for bromine's dominance as a hot tub sanitizer, but the most important is the fact that bromine is more active at higher pH range than chlorine.
Chlorine exists in two different forms - free chlorine (HOCI, hypochlorous acid, the good and powerful sanitizer) and hypochlorite (OCI -, the much less effective ion). At a pH of 7.5 there's about 50 percent of each.
That 50/50 situation occurs higher up the pH scale (where hot tubs tend to opperate) for bromine. As a direct comparision, at a pH of 7.5, bromine (HOBr), active to inactive.
In a hot tub enviroment, with higher temperatures and agitation from jets, pH tends to rise into the 7.8 -8.2 range. At that level, bromine produces much more active sanitizer than chlorine, which loses its effectiveness at higher pH.
See the chart below:
|
Chlorine & bromine sanitizers Vs. pH |
HOCI: Most active, powerful form of chlorine sanitizer |
OCI: Weaker chlorine sanitizer |
HOBr: Most active, powerful form of bromine sanitizer |
OBr: Weaker bromine sanitizer |
|
7.0 |
76% |
24% |
98% |
2% |
|
7.2 |
66% |
34% |
96% |
4% |
|
7.5 |
50% |
50% |
94% |
6% |
|
7.8 |
33% |
67% |
87% |
13% |
|
8.0 |
24% |
76% |
83% |
17% |
