There is no catfish that will eat actual waste, they all require feeding of some decription depending on diet and will not just survive on the scraps left by other fish.
The only creatures that can clean your tank are things like shrimps snails and small crabs but these are unsuitable for 99% of FW set ups.
As long as you make sure that the plec is actually an algae eating plec and not a carniverous one.for your algae problem, you could widen your choices on more exotic plecs to add to your tank. i dont know how much a 32" x 7" holds but you know what i mean