If he didn't come like that from the pet store, then you obviously have at least one nipper in there. Could be anybody, really, from that gourami to the tetra. You'll need to keep an eye on it and if any appear to become a problem, you might want to consider removing them from the tank. As well as that, keep an eye on the health of all your fish - particularly their fins. The smallest tear can lead to fin rot which can lead to a mass die-off.
Which reminds me - you probably should have stocked a little slower. Although your parameters are probably fine, the more bio-load you add in one go, the more chance there is something can go wrong. You might want to consider a quarantine tank. We have a small tank which is set up permanently for quarantine of new fish (for a couple of weeks, to ensure they're disease-free), as well as a smaller tank as the 'infirmary' so unhealthy fish can be separated and treated.
Anyway ... the tank looks great. Love the plants! I'd like to see a shot of the whole thing.















