Seeing as there seem to be so many folks here that have Columbian Sharks, I was just wondering... what are you feeding them?
I seem to have to vary the food I give mine quite a bit. One day they go nuts over HBH Lobster & Crab bits. The next day they won't touch them, but they'll tear into freezed dried blood worms like a chocoholic into a bowl of Triple Chocolate Ice Cream. The next day they take algee wafers away from the cories. The day after that, they attack a tubflex worm cube like they haven't eaten in a week. The one thing that the don't seem to have interest in at all is other fish. But that's not a bad thing...
-Phroge