My 20g H, Curviceps

[fishwatcher]

I am wanting to get a mate for my curviceps (dwarf flag cichlid), but I'm not sure how to sex them so I don't know if I have a girl or boy, or how to tell what they have at the store.
I am planning on keeping them with a few cories I have in there already, and a small group of rummy-nose tetras.
What do you think?
Thanks!!