I too have no direct experience with this fish (we have a couple members who I think do, if they see this thread) but there are some observations that can be made.
The first is the environment. Being Lake Tanganyikan, they need hard water. They are (unusually here) nocturnal feeders, so dim lighting is needed. They need some rocks (not sharp ones) for security. They live in large groups. Marc Elieson, a cichlid authority, says that in small groups of 4 they can manage but only if there is only one male with three females. Marc says you need 100+ gallons for 6-10 fish.
The afore-mentioned points are important, because fish can be stressed when conditions are not to their liking. And stress almost always eventually causes increased aggression. And here we come to what Jaysee mentioned about things changing. This is why the proper environment, water, tank, other fish, etc is so crucial for fish.
Hope this is of some help.