Although bromine is not very sensitive to pH, it is still advisable to check its level regularly. The ideal would be between 7.2 and 7.8. Above 8, bromine loses some of its effectiveness.
Water temperature is not a problem. Bromine is resistant to heat. It is for this reason that it is recommended for spas and heated pools. However, the higher the heat, the more regular bromine treatment is required.
Remember, water treatment is just one of the steps in maintaining a spa.