Mollys need s bit different care than the run of the mill livebearer. First, most people think mollys, and several other livebearers in pet stores, are normal size adults and nothing could be further from the truth. Fact is if given the correct environment, food and space 4" mollys are the norm. Secondly, mollys require a diet heavy in greens. I use algea and blanched peas cut in half. Prepared veggie food works as well. Third, mollys need some salt content to the water. I use a tbs per 5gal of solar salt. Other livebearers tolortate salt just as well. Forth, molly fry need to be removed from the parents and reared in an appropriate size tank. You can start with a 10gal, after 6 weeks move to a 20L. In summer, an outdoor kiddie pool works well. Next molly fry need live bbs the first several weeks with green food to get them started and growing quickly. Last of allMollys need good filtration, but not too much current. I catch them all the time on vacation in the estuary where water flows in and out with the tides.
Just an fyi, a 4" females molly throws a lot of young. If you're serious about breeding some to sell, breed some good breeders first.