When you are done treating the fish with copper how do you return the fish with out introducing copper to the main tank. Or will a little bit that is still on the fish be ok …
I’m not really sure.
If it were me, I’d could get some of the display tank water (i.e. whatever gets taken out from a water change) and put that in a bucket/tub as an intermediate step between the treatment tank and the DT. That would act as a rinse.
The rinse should be fine.
Most fish stores (online or local) treat their tanks with copper. Since fish are acclimated with tank water the cooper is diluted. Then the fish is netted and no copper is introduced to the tank. Never add water from any fish store on online source to a reef tank. They all use cooper to ensure the health of the fish.
Good to know