Why quarantine for weeks if using copper?

[Lionfish hunter]

If parasites like ich and velvet fall off the fish in less than a week, and copper kills any new free swimming parasites. Why does everyone recommend to quarantine new fish for weeks even when using copper? Shouldn't all the parasites fall off within a week, and all free swimmers be killed if using copper? Leaving the fish parasite free ready to go into display?

 

[Dilan Patel]

I explained the fallow procedure not copper my bad.

 

[reddogf5]

I believe you are correct, the parasites fall off in 7 days, the extra week in copper is "just in case" from what I've read. "just in case" because an extra week in copper is easier than getting ALL the fish out of your display tank and leaving it fallow for 6 weeks to 76 days, while you treat and house ALL the fish somewhere else.
Then they generally recommend observing for another two weeks. Technically you don't need to do this just for ich and velvet I believe, it is just to make sure nothing else is wrong with them, and make sure they are healthy before being introduced to the main tank.

Of course I'm just repeating stuff I read on the internet, so take it with a grain of salt

 

[Tamberav]

If parasites like ich and velvet fall off the fish in less than a week, and copper kills any new free swimming parasites. Why does everyone recommend to quarantine new fish for weeks even when using copper? Shouldn't all the parasites fall off within a week, and all free swimmers be killed if using copper? Leaving the fish parasite free ready to go into display?

It is all explained right here:

Copper treatment

EDIT: Taking the Hanna copper checker's margin of error into consideration, we are now recommending 2.2-2.3 ppm for Copper Power. This ensures that the copper level is "just right" i.e. not too high, not too low. (y) Copper treatment (updated 5-16-2023) What It Treats: Marine Ich (Cryptocaryon...

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