Hi
Ive had three congo tetras for about 5 months now, they are about 5cm long and the colour is fantastic. The are active fish with long fins. they live in a community with dwarf cichlids and tropical fish, the smallest fish in the tank is golden barbs. The congo's ignor all other fish except my giant danio's who they shoul (?showl) with. They havent been aggressive at all although one did bite my finger and im sure it had teeth.
They are fantastic fish with amazing colours.
I think they like good water quality and you need to find strong healthy specimens, ive seen some really dull ones. You also need aquaglo tubes to show them off at their best.
Most of this is from my limited experience but they are brilliant fish and very cool.
dave