I acclimated four black mollies to saltwater about a month ago and into my quarantine they went. Two of them died during the first night. The other two survived but all of their fins were tattered badly.
After 31 days their fins have mostly healed, but the smaller molly still has a frayed tail. I thought I'd keep them in the quarantine until the tail looks good, then ... a few days ago a brand-new rip appeared on the larger molly's dorsal fin along its rays. They do chase each other during mealtimes and it's possible they had bitten each other while I wasn't looking. I thought they were females but it turned out they were both male.
There is no visible sign of infection on either fin. No whitish growth or redness (though I doubt if I'd see any redness even when it appears because the mollies are pitch-black).
By the way, in the other compartment of the quarantine I have a springer's damselfish. The fish has always looked healthy. All the fish are eating well.
Ich and velvet are ruled out at this point. I don't think there are any flukes either, though I'm not absolutely sure.
Is it possible some kind of illness is hampering the recovery of the smaller molly's tail? Or ... maybe the smaller molly's tail will never heal completely?
Should I treat them with meds, leave them without meds in the quarantine until their fins heal, or just transfer them to the display? If medication is necessary I have MetroPlex, KanaPlex, Furan-2 and Melafix for possible fin treatment.
Thanks!