The fact that you use bromine is not relevant to whether you use muriatic acid; the fact that it's an indoor pool makes avoiding the fumes harder.

Standard muriatic is 31% HCl, and fumes badly. 15% HCl would be much easier to handle indoors. BUT, you have to make sure that the ONLY thing added is water to dilute. If there's any kind of detergent or other additive (helpful when using acid to clean brick, etc), then you must NOT use that acid.

Otherwise, muriatic will work just fine to lower pH. However, read the muriatic acid page linked in my signature.

BTW, the idea that plaster or gunite walls cause high pH is true for possibly a year after construction. After that, not.