hi, sorry ive no idea, some people say that ph of the water has something to do with it,
my ph is about 7.4 and out of a bath of 6 platys 5 were female.all the best with your fry donna .
Have all the batches grow up to maturity yet? Sometimes males look like females for a long time.
Also, you should get more females. The recommended ratio for Livebearers is 2-3 females per male, since the males are mating machines. This way each female gets a break.