Theoretically you could fill the tank with them, BUT remember that you have to be able to provide food for them or, like anything else, they will starve. Also remember that inverts do NOT remove nutrients from the tank, they only change the composition of it, so if you are having an algae issue for example, the inverts will help battle the algae, but finding the reason for the algae (over-feeding, too much light, high bioload, etc) is the true solution.