Welcome to our forum.
Is it be possible that your bromine floater isn't opened up, that it's still screwed all the way in?
I'd try shocking it. Bromine can take a long time to read anything when you start up fresh. I don't use the the chemical "banks"; but one fast shock of MPS or Chlorine takes care of it for me. You need something to help oxydize some of it initially - the MPS will do it.