There are a ton of nano fish you could do. Scarlet Badis, Clown Killifish, Chili Rasbora's, Ember Tetra's, Endler Livebearers, many of the Pencilfish (I keep Purple Pencilfish), Dwarf Anchor cats, Neon Rasbora's, Burmese Rosy Loaches, and a ton of other nano's.