Fish for a 17 litre tank

Question
Hello, I have a large peaceful community tank which has been running happily for 10 years. It's mostly a clean up crew and lots of Cardinal tetras and I haven't branched out into anything very clever.
I bought a 17 litre hospital tank, but have never needed it and I would like to run it as a freshwater tropical tank perhaps with an easy going plant like a cutting from the polysperma in the main tank.
I know it's a tiny tank but I was wondering if you could recommend a pretty fish, or pair of small fishes that would live happily in there...anything but a Siamese fighting fish.
I've been looking and looking and everything likes to be in groups, or would grow too big, or needs too much room. The happiness of the fish is paramount. I hate it when people have one lonely neon tetra or something :(
I feel sure there's got to be something! I'd like as much impact as possible from my little fish.
Thank you very much for your time :)
Liz

Answer
Hi Liz,
A 17 liter tank is too small to fit any fish but a betta.  The small fish that I can think that will fit in that tank are all schooling fish.  You can try 2 mollies or 2 platys but that is still a hit and miss.  It will also be hard to maintain that tank because its so small and gives no room for error.  Anything that goes wrong with the water will effect the fish rapidly whereas a larger tank takes time and allows you to have time for preparation for treatment.  Have you tried considering a 10 gallon tank?  You can keep small fish in schools in a 10 gallon with no problem.    
-Matt-