Self sustaining tank?

You could do it. Smaller display, lots of live rock, huge fuge, and something like a wrasse or mandarin to eat the pods. Few crabs and snail for waste and algae, and you're good to go. Would need top offs though. You couldn't truly do it with corals though, eventually they would use up the nutrients.

 

I guess I should have elaborated a little. In my 29g I had almost 60lbs LR by the time I was done. In my 5g I have 10+lbs LR. The LR is lacy so there's more surface for bacteria. My stability comes from my LR and sand. I do have higher nutrients than let's say an SPS geared tank but the balance is there for what I like to keep. I dooooo need to do something with all of these amphipods though :/