Put fish in it.
takes much more consideration (and money, and research) and you still don't get to have only a few fish. But cool!!!
for sure. Start learning about nano fish. Have more little fish in a small space compared to commonly found /sold fish. Check out msjinkzd.com "Invertebrates by Msjinkzd - Specializing in invertebrates and micro fish from around the world." She has pics, (also sells), is a co-author of a book about nano fish and is a knowledgeable and kind person to work with.
What do you like?