:Is it a bad idea to mix different breeds of turtles together? I am planning a small pond with red ears, yellow bellies, and red bellies.....any thoughts?
It depends on species. It is a bad idea to mix species that have different environmental requirements AND a big NO NO to mix species from different geographical locations (IE Asian turtles with North American species).
The species you listed should be alright together. They have about the same requirements.