Silver Hatchetfish Aggression?

[nmonks]

I have some common silver hatchet fish, four to be precise. One thing that is surprising me is how aggressive they seem to be to one another. The two larger ones fight a lot, to the point where they pull scales off one another. Is this normal? Would adding more hatchetfish help?

They're otherwise lovely fish, and in particular seem to enjoy following the glassfish around (much to the annoyance of the glassfish!)

Cheers,

Neale