Even a small Lionfish will likely eat even a decent sized Molly, and the Lion will grow quickly, so I still don't think this is a great mix.
But, as far how to QT them, I searched, and I got replies from Jay H. that seem to be a little conflicting. Here, he says that QT is important for all livestock, and notes that many Mollies are breed in brackishwater, not fresh, and should be QT'd (and he means a copper based, medicated QT, typically):
https://www.reef2reef.com/threads/temperate-atlantic-compatibility-with-reef.1166000/post-14464026
And here he says to just raise the salinity, noting that most ectoparasites cannot go from fresh to full saltwater:
https://www.reef2reef.com/threads/freshwater-molly-qt.1134271/post-13954778
He does note that freshwater Mollies can bring internal parasites, though not as easy to transmit to other fish.
If this was me, I'd do the full QT on them out of an abundance of caution, if nothing else.
@Jay Hemdal do you have a minute to clarify if the OP should or should not do a medicated QT on Mollies converted from fresh to saltwater? Thank you for your help!
