Mollies have to be acclimated like crazy. Not even close to a good idea. They’re a freshwater fish and although they can live in saltwater, you’d have to bring your alkalinity way down firstYou could add a few (1-5 or so) male molly(ies) to test the system and don't feed it/them for a week. Then start feeding a single flake per day.
If parameters jump up then right back down, that is a good sign. even better if you get no spikes. LOL
Once you get some $2 FW mollies to live for 2-3 weeks or so you have a very good indication the more expensive and delicate marine only fish should thrive also.
And the LFS might give you store credit.
my .02


