MadSci Network: Chemistry

Re: When you add bromine to a hot tub, does it affect the pH at all?

Date: Tue Jul 11 02:45:17 2006
Posted By: Levy Pascua, Grad student, food science, bakery industry
Area of science: Chemistry
ID: 1149011490.Ch

Hi Ross,

It's true that bromine is a kind of sanitizer or disinfectant used to kill bacteria, to kill algae and also to break down body oils, sweat, lotions, skin flakes etc. - also known as 'bather waste'! It is used in spas like chlorine. Bromine belongs to the same family of chemicals as chlorine and so it behaves in a very similar way. It kills bacteria and algae in the same way as chlorine. Depending on the form of bromine added to the water it forms its own equivalent of chloramines called bromamines. Bromamines, however, are not nearly as bad as chloramines. Bromamines do not smell as much and they are actually a disinfectant in their own right, so they enhance the bacteria killing capability of the bromine. The result is that you can achieve the same disinfectant effect at lower chemical concentrations than when using chlorine. Bromamines are also more tolerant of high pH and high spa water temperatures. Therefore it is not used in hot tubs to change the pH but is being used for its disinfectant capability. Being tolerant of high pH and high temperature it is more effective in killing microorganisms.

Until then,

Moderator's Note
Liquid Bromine can form hypobrmous acid (HOBr) and hydrobromic acid (HBr) when added to pure water:

Br2 + H2O → HOBr + HBr
The products can dissociate to release H+ and lower pH. However, a variety of factors, including starting pH of the water, exposure to UV light and presence of other agents in the water (amines, for instance) affect whether HBr and HOBr are formed, versus bromamines. In most hot tub systems, there is sufficient material from bathers and contaminants to skew towards bromamine formation; most disinfectant tablets also include amines or other chemicals for these reactions to occur.

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