What kind of food are you feeding? If it's a floating food, like flakes or pellets, it could be that the catfish are reluctant to feed at the surface. For my bottom feeders, I use sinking wafers. I also use a syringe to direct thawed frozen food to them (by releasing food close to the bottom).
You can get the same effect with flakes by putting a pinch of them in your fist, and releasing them closer to the bottom. That way the flakes get water-logged. Some will sink to the bottom right away, some will dance in the flow in the water column, and some will float to the surface. It's also very enticing because the flakes seem to dance like live food! Mmmm. Fish at all swimming levels should be able to benefit from this method, I've found.
Hope that helps!