Three ideas come to mind for a species only tank:
1) A cory only tank. One or even two of the dwarf cory species - habrosus, hastatus, pygmaeus. Habrosus stay along the bottom more like the full size cories, while hastatus and pygmaeus use more of the mid-water column. I've had habrosus breed a few times, and with hastatus I got one fry who unfortunately didn't make it with other fish in the tank. Haven't had pygmaeus myself. In this set up, I would do habrosus and hastatus - probably 6 habrosus, 8 hastatus.
2) Sparkling Gouramis. I haven't had luck breeding these (and I no longer have them), but I've read of others who have.
3) Dwarf pencilfish or Beckfordi pencilfish. I have the dwarfs in a tank with WCMM and if there's any breeding going on, I haven't seen it. But I also have a red variety of the Beckford pencilfish in another tank, and have had 6 fry survive so far from a single pair of adults. Hoping for more.
Here's another one:
4) Peacock Gudgeons
Last edited by SueD; 06-11-2019 at 04:04 PM.
Reason: added idea