I have a beautiful male Missouri longear and two male Western dollar sunfish in a 57g tank. It's a strange dynamic: the two dollars constantly police each other, but the much larger longear seems to keep them in check. They share the tank with an geriatric pearl gourami, two diamond tetras, and a bunch of otocinclus. The tropicals are leftovers from an older planted tank, and I decided to allow them to expire naturally rather than putting them through the stress of "donating" them back to a store. I might restock the otocinclus - they seem to like the temperature around 70 and get along well with everyone (as otos always seem to).
When the larger tropicals are gone, I'd like to add one more native species. Something large (or inconspicuous) enough not to be harassed by the sunfish but not so large that it overwhelms the system. Maybe some darter species? I'd be grateful for any recommendations.
The tank currently has a sand bottom and is moderately planted, but that could be adjusted.