Some kind of small to mid sized south american cichlid might be a good fit for you. I would look into blue acaras. They get to your prescribed size of 5-7", personable, entertaining to feed but not too predatory that they will attack your corys.
A 55 is adequate space for a small group of them along with your cory cats. I would look for captive bred acaras instead of wild caught because they are usually more resilient, better adapted to aquarium life. Wild caught acaras frequently require strict water conditions ie high acidity and restrictive temperatures.
A 55 is adequate space for a small group of them along with your cory cats. I would look for captive bred acaras instead of wild caught because they are usually more resilient, better adapted to aquarium life. Wild caught acaras frequently require strict water conditions ie high acidity and restrictive temperatures.