I've loved and raised livebearers off and on for 50 years. I also grew up where the Molly was native to our waters. There are those that will disagree with my methods but I don't care. This has been very successful for me on adult and fry survival.
First, if you're serious about just raising livebearers you need to dedicate the tank to just them. Livebearers will adjust their water with their biochemistry that is a little different than egglayers.
They do best in 7.2 to 8.2 pH water with a KH of 8 to 20 and the ideal temp is 78F.
Their diet (being a tooth carp) needs to be about half animal & half plant matter.
Now here is the most important fact with especially swords and mollies. Their natural habitat is estuary streams(meaning close enough to the ocean that tidal forces mix salt and fresh water at various times. I have found that keeping salt in their tank at a solution of 1 tsp per 5 gal give maximum health and fry survival. This also works well with Guppies.
A fully planted tank with lots of fine leafed species such as Ambulia give them plenty to munch on and good hiding spots for the fry to hide and grow in.
I have found it is much less stressful on the momma and babies to be born and raised in the tank. An old established tank with lots of bio film, plant matter and accompanying infusorial rotifers give the highest survival and growth rate for the fry. They can take frozen or fresh baby brine shrimp right away.
If you keep the adults well fed, predation of the fry is kept to the deformed and weak fry that need to be culled anyway. About once a year the adults need to be rotated out and new stock added to minimize inbreeding. Hope this helps. OS.
