If territories is what you are worry about then a simple rearrangement of decor would solve that problem. Also try adding the fish at night and turning out the light after doing this. This will give the fish time to adjust to the new tank under the cover of darkness and when it starts to get light, there will be new fish and the tank will be different.
As Star_Rider said already, vertical visual barrier help a lot not only in breaking line of sight but also in giving the fish a sense of security.
I don't think you will have a problem in a 120g.
As Star_Rider said already, vertical visual barrier help a lot not only in breaking line of sight but also in giving the fish a sense of security.
I don't think you will have a problem in a 120g.
