Is this because the free swimming stage could attach to the frozen Cod? Scallop is an invertebrate she shouldn’t become a host, correct?Be extremely careful doing this. I had a fallow period fail because of what we could only determine was frozen food keeping the life cycle going somehow. I had a BTA at the time and was feeding once a week with small chunks of frozen scallop and cod fillet. Otherwise, the tank was fallow for the (I think it's 30 days for velvet?), had no cross contamination, and the QT was in another room so no aerosol transmission.
I would dose straight NO3 or PO4, or use a pellet or flake food. I would not add anything fresh or frozen to the tank.