Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
The smaller fish would be a better choice. 40 breeder is only 3' long. Congos are about the largest I would add.
Since Congos are African, did you want to stick to African fish?
Upside Down Cats (make sure you get Synodontis nigriventris, they are pretty peaceful. Some of the others like the mostly black ones are quite aggressive, and get larger)
Kribs- there are several species, do some research.
Jewel Cichlids? (Feisty fish, probably not right for this small tank)
Anomalochromis thomasi 'African Butterfly Cichlid' (these guys bred for me several years ago)
Butterfly Fish (the top of the tank predator)