Mollies are one of the vegetation needing fishes, it is essensial to their diet. So whether its tetra-veg or some other type of greens this will provide them with optimum fertility and vitality.
I do not use any salt in my aquarium and have had no problems with the Swords breeding. Temperature can play a factor as I understand it I have mine at 25C. I do not know about other species, they may need a couple degrees one way or the other.