nate

I just took all of the corals out of my nano reef tank and moved them to my reef set up in my 60G. So I have an empty 20G tank just chillin in a corner. Any ideas on what to put into it. Anything helps here. I don't like to just have empty tanks sitting around.

sirdarksol

Depending on how much work you're willing to put into it, you could set it up as a small oddity aquarium and keep something you couldn't keep in a normal community. If you like inverts, you could keep an invert (or a community of smaller ones) that wouldn't do well around other tank-mates.
Or if there's a coral that doesn't do well with most fish, you could keep that and a small cleaner crew.
With a smaller tank, it can be interesting to come up with a way to highlight a particular species.