Holding fish in a tote during a fallow period is not easy to do.
You can shorten the fallow period by raising the temperature. It becomes as short as 45 days at 81 F. However, the animals left in the tank have to be able to handle the higher temperatures.
Yes, you can drain the whole tank and fill it with tap water (don't need RO/DI for this). Let it run for 48 hours. That will take care of ich or flukes. However, if you have any animals in the tank that you need to remove to do this, they will still be carrying diseases.
If the tank does not have any invertebrates in it, you can just leave the fish in there and run the hyposalinity treatment that I had mentioned.
For keeping this issue from happening again, you should quarantine all new fish:
2024 Quarantine Procedures Jay Hemdal David Scarborough Protozoans (Cryptocaryon/ich, Amyloodinium/velvet) and Metazoan trematodes/flukes are by far the most common parasites found on newly acquired fish. A carefully managed, proactive quarantine process can effectively eliminate these...
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Jay