I saw your pic of your mystery fish (it's been a while, so I hope I'm remembering correctly). It very well may be a mextico, but it also strongly resembles another Thorichthys species, the maculipinnis (used to be called elliotti).
There is a wealth of info on the little mac's. Also, try a search for T. aureus (or aureum). The care info should be about the same for all these species as they are closely related.
HTH