Should i ghost feed the display tank during fallow? Also, should i do the fallow for 6 weeks or 76 days?It’s best practice to use clean saltwater instead, so that you are carrying over as little parasite-load as possible. Mix fresh saltwater and seed the QT with biospira or another bottled bacteria to prevent ammonia build-up.
And to answer your other question, there are many things you can do to help manage parasite-load in your DT, including running UV at a very slow rate, increasing flow, daily vacuuming of the substrate/tank bottom, feeding live and vitamin-enriched foods, etc.
But, there is no reef-safe treatment currently that will eradicate it. Treating the fish and going fallow for 6-weeks (76 days for ich) is the only way to be rid of it completely.