I haven't seen anyone mention but I'm partial to the other members of the goby family, not just the firefishs in it. I have a bar (or zebra) goby that hangs out near the front of the tank and about midlevel all day. I also have a school of three neon gobies that hide for most of the morning and afternoon but then come out and swim all over. I've never seen any of them take even a remote interest in chasing other fish, only chasing their food.