Platy Changing Gender?!?!

Yes it is. It is an old wives' fishkeepers' tale about livebearers changing sex. Some males are very slow maturing, and as you know all fry look female until puberty.
I don't know if the same thing happens with livebearers but subordinate cockatoo apistogramma males often take on female appearance to avoid the attentions of the dominant male in a tank with multiple males. If this is possible with livebearers perhaps pheromones secreted by the fully adult males suppress puberty in the male fry 


Very old females sometimes develop a gonopodium, possibly in the same way that post menopausal human women can develop some male characteristics, but they never become functional males.

Very interesting indeed. Would there be room in your tank for more platies (hopefully definitely female) to balance the ratio out a bit? Alternatively, if not, and if you don't have any particular plans for the bigger, unused tank, would you consider using it to accommodate a larger group?

Let us hope that things continue to remain calm.