A royal gramma is a great addition. I love mine
I found with my firefish goby he mostly hung out in the middle of the water column. Of course he may compete with the other goby for somewhere to sleep but once territories are established everything will be fine they're pretty mellow about stuff (unless of course it is another firefish goby). Anyway, all my fish are tiny so I don't have any other suggestions to give you
Christy
