Fish that work in a 10 gal are guppies, betta, neon tetra, ember tetra, dadios, mosquito aka chili rasbora, dario dario aka scarlet badis, sparkling gourami, celestial pearl danios, pygmy cories such as corydoras hasbrosus, kuhli loaches (smooth substrate for burrowing required). You can also do shrimp, mystery snail, and nerite snails.