You can grow anubias in a low light tank too, for more variety. I had a 125 gallon tank a few years ago, with mostly platies and guppies in it, and the platies soon dominated the tank. I found that guppies couldn't tolerate as high a temperature as the platies, and I had this one at 80 F most of the time. As far as sex goes (fish sex, that is) it is extremely obvious which is the male and which is the female - just look for the very dark anal spot on the females, and their bigger size, less svelte figures, and dull coloration. Plus, it is really up to the males to determine who is a female, and I found they do that instantly and continuously.