I agree with flchamp. Pygmy corys are tiny, but active, and need to be in groups. What fish do you have in your larger (20g?) tank? Is it possible to rehome a couple to your smaller tank and stock pygmy corys in your larger?
150g long S Amer cichlid; 90g C Amer cichlid; 90g Malawi cichlid; 40g Tanganyika cichlid; 29g "Shellie" cichlid; 29g Pea Puffer. 6,500g koi/native catfish pond; several smaller ponds