If you want more than one firefish introduce them at the same time. I have two and they have never shown aggression towards each other or any of the other fish. Very peaceful. The both sleep cuddled up next to each other in a cave. They eat anything I put in. I've never seen them jump but when they get scared they dart very fast around so I do have a screen top I keep on my rimless. When I first got them they hung around a cave on the right side of my tank towards the bottom, probably about 4 - 5 months it seemed. Now they move all over the tank, mostly mid to lower level but don't swim back and forth, mostly hover. Good luck, they are great fish.