whenever i added new platy colors to my tank i always added in 3s 2 females per 1 male...My first pair I only had the two, when I separated the female b/c she was prego, the male got all lonely and swam around looking for her at the end of the tank nearest her tank...also, if it is just 1 male on 1 female, your female will get all stressed out from the constant attempts at sex...which is why you need at least 2 females and lots of hiding places for the females so they don't get so stressed...that's my experience at least...