That’s what I thought too at first, until I read up more in depth about common parasites like ich and their life cycle.
The reason tank transfer works so well is because they’re exploiting the time during which the parasites on the Fish drop off into their free-Swimming phase(which is when copper is able to kill them).
Usually this starts to happen after the first 72 hours, during which time if you’re QTing only one Fish at a time, the ectoparasites that may survive the copper dose are unlikely to reinfect the same Fish within such a short period. Before they can potentially repopulate, the week is over and I transfer the fish to the Paraguard bath to get rid of any potential loose ends and I must say the product has not let me down so far.
The medicated bath for a few hours really seem to get rid of all the nasties, and the freshwater dip before finally introducing them to the main system serves as some insurance lol
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