I've tired a few times to keep swords, but they all seem to die, and I never see any young from them. Every other fish I've had seem ok, but swords (and once with mollies) never last.
This. If you don't have hard alkaline water, you will have less success with the swords and molliesSwordtails, like most livebearers, do best in hard, alkaline water. My swords usually faded away after a few months until I realized it was my soft tap water that was killing them.