Hi Dustin,
I have a pair of both the purple and regular firefish with no problems at all. I do have a 120 though. Just make sure they have bolt holes on opposite sides of the tank

Also...make sure you have a cover of some sort. Firefish have a reputation for leaping out of the water. I heard a clunk one night and found one of them in the overflow. He bounced in there.
They are very pretty fish and offer some good activity, even if it is a flash of color and a small cloud of sand as they dive into their holes.