CichlidFish.com - Fish That Think.

I have an Apisto pair in a 5g, they needed some respite from a busier tank.  But it takes individuals, these 2 get on like a house on fire and breed like rabbits, so I left them that way.  Another pair that I tried for breeding nearly killed each other in a slightly larger tank, but then they already ruled their 33g tank, putting Tiger Barbs & Serpae Tetras in their place.

I wouldn't suggest anything bigger than that, Rams perhaps, but you really have to keep on top of their water which isn't so easy in a smaller tank.

if u have harder water, than a pair of neolamprologus brevis would do well if you stay on top of water changes.