Well your tank is a bit crowded and the danios are hectic swimmers so they probably just need more room. They are also known to be nippy. FYI colored skirt tetras are dyed with needles and your lobster needs at least twenty gallons, 30+ being perferable and may eat sleeping neons. Also what kind of pleco do you have? Many will out grow a twenty nine. Sorry this mostly :OT: Anyways watch and see if they are doing serious damage. If so you might have to remove one or the other.
well the lobster is tiny and in the 10g cause my brothers 55g tank didn't cycle properly and he lost like 4 fish. Once its better its going back in the 55g.
The pleco is tiny right now (2") but if it gets bigger it can go in the 55g too
P.S. The lobster just molted too soo he's being kinda shy right now
It was strange because the zebra's weren't bothering the skirt tetras I have and they actually came in defense of my neons. Those tetras stick together