I got my Serpae Tetras accidentally, too, due to my bad memory. I thought I'd read they were peaceful! Mine actually aren't too bad. Occasionally one might chase one of my Bleeding Hearts a bit, but never far. They haven't nipped at any fish, but I don't have any slow movers in there, either. If they get obnoxious when I add my Angels, they'll just end up banished to my 10 gallon.
Their "feeding frenzy", like nmonks mentioned, is fun to watch. At dinner time I have to close the cover fast, or I get splashed in the face! That goes for the Bleeding Hearts, too!