my balloon mollie is pregnant please help.

i know nothing about fish other then my research online in the last couple of days....


i recently bought 3 balloon mollies and from online pics i think i have 2 black females and one white male....

one of the black mollies was pestering all that other fish incl. the other mollies and ended up killing my young angel fish so we separated it from the others and it went to a friends house and then came back (she couldn't keep it), why was she being mean and the other 2 weren't?

when i brought the mean black mollie back home and saw it beside the other black mollie i realized the one in my tank looked like it was twice the size in the belly, and the last few days she has been floating up at the top of the tank. i know shes not overfed because the other fish and mollies are ok.

what should i do. do i need another tank?

thanks