I've kept Ellasoma, two species. Why the Latin? There are two very different pygmy sunfish groups, which behave differently, look differently and need different conditions. The Ellasoma group is the one more often seen, and I have had E okeefenokee, and evergladei.
I caught the okeefenokee myself, by lifting rotting logs in a few cm of water and jamming a net under, scraping along the wood. I ten sorted through the mud and debris in the net, and removed pygmy sunfish, Heterandria formosa ("least killifish" livebearers - a fish you don't realize you want, but that you should buy if you see it) and ghost shrimp. In the open water around, also shallow, there were bluefin killies, sailfin mollies and Gambusia affinis. It was a lovely place.
The story has a point!
They like darkness, and they like to hide. I found them so beautiful it was worthwhile keeping them even if I didn't see them every time I looked for them. Kept in the open, their colours faded, but in jungle-like tanks, they were fantastic things.
They never adjusted to non live food. They did well on live freshly hatched brine shrimp and daphnia, plus the micro-organisms they got from the wood and plants. Right there, you see why something so pretty is so rare. They tended to react to movement in their food, and would let prepared food float by and rot. They are micro-predators tuned to movement, although I have heard of people getting them to eat specialty foods that didn't move. I had them for 2 generations and I never succeeded in that. I was hoping the tank raised ones I had from breeding them would be easier, but they weren't. They were also all males, which stopped my plans to keep them going both times.