If you are using bromine in the tub then you need a special FAS-DPD test that is calibrated for bromine (taylor K-2106 is the complete kit. I forget the number of the stand alone bromine FAS-DPD test for bromine). You can alwasy use an OTO test since you are only interested in total bromine. Many of the cheapie test kits have a problem testing pH in a bromine system because of insufficient halogen neutalizier in the reagent. The Taylor pH reagent does not have this problem.