Hi Bob. The problem with Live bearers is that yes they are almost always pregnant and if there is a Male present... guaranteed. Gestation is average 28 days so count out on your calender and start watching her/them to square off at the front underside. She will start hiding a day or so before dropping her fry too. 2ndly, to help the females combat the constant male harassment, a "harem" is best, so 1 M to 3 Females BUT that means way more fry potential. Kind of a vicious circle. Depends on if you can grow them out and sell them to a LFS or not.
Another way that works for Moms/fry (this is what I used to do) is when you know she is close to do a water change with dechlor that evening and set the water at no more than 2 degrees below your tank water temp... do about 30 %. When done shut off your lights for the night... so you are creating a cooling evening rain effect. If you don't have floating live plants, lay a few plastic ones on the surface to create a sense of security/hiding area.
In the morning don't turn on the lights... If you can peak in the back corners with a flash light around the rim of the tank... the fry when first born will be on the surface along the rim, in the corners. (still kind of stunned from the process but it won't take them long to get their bearings).
Feed everyone else in the tank at the far end of the tank, sinking food preferably... (they are so curious they come see what you are doing) so send them all far away while you work on scooping fry up with a net into a container of tank water to move to another tank or straight into the fry net. Make sure the fry net or baby tank if it's floating stays secured above the surface.... it takes only a few minutes for all fry to escape and become dinner. At some point you will have so many that you will just add lots of plants and provide cover and will likely have 1-5 survivors each drop,... letting nature take it's course. That's what I do now.
Release fry into the main tank when they are bigger than the biggest mouth that can eat them.
Good luck... keep us posted! Don't hesitate to ask any questions here.
