Here's the sales thread where I found the S. petricola
It sounds like a good seller who is offering the fish.
I have been pondering this setup some more. One variable that I have wondered about is additional fish selection. A few other ideas came to mind for fish to swim around in the mid-level/top-level of the tank. I wondered about rainbows, or West African tetras or some kind of barb. The best solution was right under my nose. I have colonies of several different livebearer species that originated from fish that I collected in Jalisco, Mexico during two different trips in 2007 and 2008. These are really great fish, but I have had them in these colony tanks for so long that I don't really think of them as display fish. However, they have beautiful appearances. I am likely to use this one, Poecilia chica
as the main shoaling fish in addition to the group of S. petricola.
What a gorgeous fish! It doesn't have super bright colors, but it has that turquoise iridescence on its flanks as well as patches of metallic gold. The breeding males develop more vibrant turquoise coloration as well as dark black on their fin margins. I got that picture above at the same location where I collected beginnings of my colony in the Río Purificación near the town of La Huerta (GPS: N 19°30'22.8" W 104°39'28.6"). I currently have about 40 of these--most are fry--in a 40 breeder. I think that I will pick out a group of about a dozen medium-sized individuals to form the school in this new tank.