Yes, the DT tank is infested with the parasite. The parasite needs a host (fish) to complete its lifecycle. Remove all fish from the DT for 6-8 weeks and the lifecyle is broken. During that time you maintain/treat the fish in a QT tank using hyposalnity (SG
of 1.009) at which the parasite cannot survive. So you kill it in the DT because there are no fish, yet the corals and inverts are maintained at normal conditions, and at the same time you kill it on the fish by breaking it's lifecycle using reduced salinity. It's a win/win (though it takes a bit of work).