I've got about 25 (?) of them in a 20 gallon long. The wolf fish analogy is apt. Imagine a school of very tiny rainbow wolf fish, except that they get along fine with one another. You needn't worry about sex ratios unless you're breeding them.
The males establish dominance through fin display, and they really put on a show. The spectacular pictures you'll see online are from those dominance displays. It doesn't happen very often, though. The rest of the time, you'll hardly ever see them. Their ability to melt into the substrate and decoration is amazing. And by amazing, I mean your tank will look totally empty most of the time. People will ask you when you are going to put fish in it.
I've got a few suggestions for keeping them long term:
- keep them in very soft, acidic water. I'd say it's obligatory for these guys. Don't add anything weird to the water either. My water is 20 ppm of hardness out of the tap and I soften it with peat. They do not like hard water or changes to water parameters.
- keep them in a species tank. Diseases that other fish can carry without symptoms can kill these guys. I lost every single one of my last batch that way. I've never seen a group of fish die so fast. All gone in 24 hours. The source fish was fine. That being said, I have kept small numbers in community tanks in the past, and they did ok.
- feed them live food regularly. I've never had trouble feeding mine pellets, but watching them hit moina is pretty fun. You'll see why they're called darters.
So all in all, they're a rewarding fish, but tricky. Keep things stable and you'll find they're quite hardy. One false move, however, and they can die en masse. And they do hide all the time. Definitely a fish for enthusiasts.
