Ian Fuller, the premiere Cory specialist in Britian, founder of CoryWorld, and a member here with the ID Coryman, instructed us a year or so ago that Corys will get all the green and algae needed from the algae and plant matter in the water of a mature tank. Corys will graze on the unseen algae and other nutrients. I myself have seen fry that had survived all the hazards to grow up unaided by the unseen nutrients in an unplanted tank and no fry food had been added. I have a volunteer lf bronze C. aneaus now in the adult tank that never saw fry food. He is their first (that I know of) to survive and grow to juvie fryhood without assistance.
I am a very proud grandmother.
Ian teaches that a good omnivore bottom feeder wafer or tab like Hikari Sinking Wafers for bottom feeders or TetraminTabs for bottom feeders will provide all that an omnivore Catfish needs. They are made to provide the special diets that omnivore bottomfeeders wants. When you go to your lps or lfs look at the ingredients on an omnivore catfish label. They contain greens and meat and vitamins, etc., for the fish.
On the other hand, some catfish owners feed their Corys algae wafers who seem to love them. But they should be considered a suppliment and a treat not a diet for an omnivore. They are formulated for herbavores like Plecs and otos.
I would not make frozen or freeze dried blood worms the primary source for the Catfish either. They make a nice treat, although again, my Corys are not impressed with frozen or freeze dried foods, because they get live black worms.
A good omnivore bottom feeder tab or wafer will provide all the needed requirements that the Catfish needs. The rest is treat. (Although I feed mine live blackworms as their primary staple and add other foods like flake and wafers to make sure they get what they need. I really don't bother with algae wafers.)
This is primarily what Ian taught us. And while I have had extended arguments with him over personal preferences, this is not one of them. It confirmed my own reasearch that I did before I was told anything else.
So what to feed your Corys? A good omnivore bottom feeder tab or wafer. Then suppliment that with what they like and eat. Many of the things being suggested here my Corys don't even bother with. They get what those things offer from other sources that they prefer.