Associated Press: Pond scum was once an aquatic nuisance that Hall Barret III once hated to see in his catfish ponds. It just might become his next cash cow. After more than 30 years, Barret is giving up catfish and becoming a landlord of algae. And he’s hoping his lease agreement with PetroSun BioFuels Inc. pays him huge royalties. The Scottsdale, Ariz.-based company wants to convert Barret’s catfish ponds into an algae farm to produce alternative fuel, paying the owner of B&B Fish …