Those flame tetras were dividing the tank into territories. They only worked with lots of plants, otherwise the weakest were harrassed to death in some corner. They also attacked guppies and the ram. The glowlights didn't have a chance against the last flame tetra, who claimed more than half of the tank for himself.My H&Ts will chase each other around, but I've never seen any actual damage done, no actual nipping, more like bumping and "Let's swim real fast through these plants -- tag, you're it!" and "I'll get you for that!" but then in a few seconds the chaser forgets why he/she was chasing. I do have a plump female black neon who claims half the 6G tank and chases others away (they keep returning) -- until yesterday, when my smaller male BN turned the tables and was chasing her everywhere. Ah, sex! But I find H&Ts to be easy going.
I just say this as a word of caution. "Peaceful community fish" sometimes just means "doesn't kill tankmates outright".