Can i use muratic acid to lower the PH of my indoor pool that uses bromine???

I have constant high readings of PH. My local pool store says it is because of my plaster or gunite pool walls. I use bromine because it is indoors. I would like to try muratic acid to lower the PH. Can I??

Where can I buy muratic acid. I bought some a Home Depot & suspect it is say 15% strength. The bottle does not say the strength.

Thanks in advance