Corys are much more active at night. Once your lights go off at night, turn your regular lighting (lamps, overhead lights) down just leaving enough light to see the fish move around. Then put them something like brine shrimp, daphnia, cooked peas (shelled of course) or even sinking pellets in and watch them come alive. I usually give mine some sort of frozen food after the lights go out and just sit on the floor and watch them scoot around scavenging for food. I love my corys and plan to have 6 or 8 in my new 75 gallon.