"Last fish" ideas?

[gobytron]

I'm 90% sure that as long as they are added simultaneously and aren't too close in size you won't see much aggression beyond establishing a pecking order.

You might be able to get away with reaquascaping your tank and adding a couple new firefish then though...

Or buy try adding some that are much larger than the ones you have in there already as this seems to make established fish less likely to get their hate on for the new guy...

I can only speak from my specific experience with paired/shoals of fish and what I've read about firefish.