I have a 60 and had 3 orange firefish. They all got along fine for several months, but when I moved and reconfigured the tank the smallest one began to obsessively pick on the medium sized one. It would get pretty nasty sometimes. Torn fins and tails and such. Then one day the one getting picked on was never seen again. I only had a percula with them who could care less what the others were doing. So I know that other firefish had to be the culprit. You probably will get different results with each fish but would be safer with 1 or a group of some size so the bullies can distribute their wrath among more than just one fish.