keep a close eye on the neon gobies. Both times I've tried to add two that weren't already an establishes pair one was always seeking out the other and being very aggressive towards it, and that was in a 150 gallon system. I figured that was more than enough room for those two little buggers, apparently it was not.
I have a 110 gallon with a purple firefish and lots of rock. Added a regular firefish about two weeks ago because I had read that I should be able to keep two in a large tank. A few days later I added a mandrian dragonet. I haven't seen the "normal" firefish since.
It certainly didn't jump (I've checked). I'm not sure if it's dead or just hiding out in the rocks.