Achieving an even sex ratio.

[Stanzzzz7]

I have a group of Rio otapa swordtails. I got them all quite young,I have a group of ten.
As they have matured they have, all but 2,turned out male.
They have bred a few times but nearly all offspring have turned out to be males.
Does anybody know why?
I presume it will be down to diet or ph or temperature?
My ph is 7.6
My water is hard
I keep the temp at 74.
I need to get more females but keep getting males.I would be very grateful if anybody knows any thing about this subject.
Thanks.

 

[festaedan]

I think the water hardness might have to do with it.
I've bred a few kinds of wild swords and there was a good ratio. My ph is right at 7

 

[Stanzzzz7]

Thanks for the reply.
I would be a little surprised if my water is too hard or ph too high as they are very similar to the fishes natural habitat.