Originally Posted by ethylenelove
Thanks, I will do that--- when will I know to separate them from the others?
It takes around 4 weeks for them to give birth and you can't always rely on looking for the black spot to determine if they are pregnant. You mention that one looks very fat so keep a good watch on her, as she gets bigger and fatter around the tummy you may notice that she will start to hide amongst the plants and she will position herself in the water so that her head is raised and tail is lowered, this is a good sign although you have to be there to notice.
I suggest you buy a net breeder, it is a square plastic frame over which is stretched a fine netting, it comes with 4 suction caps and is placed inside the main tank, I don't know where you live, but here in Australia the net breeder is only about 5 bucks. Keep the mother in the main tank until you think she is acting strangely (see above) then place her in it. She will have the babies in there and they will be safe from all the other fish but you will have to remove her as soon as you can, otherwise she will eat a few herself, you can leave the babies in the breeder for a couple of weeks but it depends on how many there are, you could have 10 or you could have 40. In the couple of weeks that they are in the breeder, set up another tank and have it running so that the water is aged in preparation for them.
Murphys Law says that you won't be around when the action takes place so don't be too eager to put her in the breeder beforehand, she may become stressed. You've just bought her so give her 2 weeks in the main tank, if she is fat already she may be 2 weeks pregnant, it's all guesswork. However, if she is still in the main tank and suddenly you notice that she is un-fat (haha), then you've missed it, but don't worry, still put the breeder in the tank and spend some time looking for the babies, they will be there somewhere, so catch them and put them in the breeder.
Good luck, keep me up to date on your progress and of course ask me anytrhing you are not sure about.