@Jay Hemdal is it possible that the larger tilefish still has flukes even though the smaller one was 100% clear during the last diagnostic FW dip I did a few days ago? I noticed the larger one's head twitching, but I can't tell if it's just irritation from the infection or if he could still have flukes.
Have you ever seen one fish be completely clear while the other is still infected? I'm thinking about doing a skin swab from the larger one, and checking it under a microscope, as I'm afraid to do a FW dip on him.
It’s possible that it still has flukes, but having one fish in the tank be cleared of flukes, but the other not be is impossible - both would reinfected if flukes survived the treatment(s). If that happened, one may just have more symptoms than the other at the moment.
I would NOT do a skin scrape - you have to hold the fish and really scrape it in order to find any flukes. One benefit of skin scrapes is that any flukes will still be alive, so their motion makes it easier to see them under the microscope.
FW dips work, but some species of fluke get so distorted that they are tough to recognize under the microscope. Formalin dips distort less, but I don’t suggest using that in homes.
I see you later posted some images - I’ll go look at them now…..