I don't really want a betta, they just seem like a boring fish to me. But i do kinda like that shrimp idea. If i did a few shrimp, how many fish could i have in there? Im thinking maybe like rasboras, tetras, or danios. Otherwise could i get something like a dwarf gourami and then a few other small fish with that? I have an undergravel filter and a power filter with the tank if that helps.