I thought of a new game plan, based off of your suggestion. I'm going to try it if the general cure doesn't work.
It's pretty much the tank transfer method. I'll fw dip everyone for a long time, then put them into a different qt tank that is clean. Then, I'll fw dip them again and if they still have flukes, I'll do the same thing over.
You can do this, however, it will not eradicate the flukes as the eggs are also laid on the fish...it's not like crypto.
My only concern is ammonia. This second tank won't be cycled, I'll probably use biospira to help, but it's going to be tough.
If you are going to transfer after 4-5 days it'll be ok. Just use something like Prime to lock the ammonia.
Do you think one tank transfer will be enough to break the cycle
No, you'll have to do at least 3
Also, I can't really acclimate them after the fw dip, because that would defeat the purpose to put them back into infected water. Would matching salinity and temp be fine for a transfer from the fw dip to the new tank?