Personally would probably not add another Bristletooth family member but a Zebrasoma species like a Yellow, Purple or Scopus could be a fine mix. Is this a 4', 5' or 6' version of the 125g ??? I currently have five tangs in my 125g though will be building a bit larger tank shortly of 187-ish for added swimming room. Also will be rehoming my to large for system Blochii Tang to a friends larger DT which will replaced with a small Hepatus Tang currently in my Frag Tank.