What are some good top dwellers? (20g High)

[Squirt]

10 lowlight tetras
2 GBR
1 Bolivian Ram
1 Sunset Gourami
1 African Dwarf Frog
6 Pygmy Corydoras coming soon

I thought that my tetras would be top dwellers but they hide along the bottom of the tank. My Gourami is all over but he is the closest to a top dweller I have. Also, I have a Golden Wonder Killifish but he is temporary because he will be a risk to my smaller fish.

 

[Squirt]

Update: Dwarf Frog died, apparently they can't live in an aquarium that tall...

 

[Mike Wise]

Personally, I think you tank is full (overly full?) as it is. Sure, you could add more but when an aquarium becomes more work keeping it healthy than being fun many lose interest in the hobby.