You should also consider a different LFS. I don't mean to be rude, but raising the temp for ich is freshwater advice, and even then is questionable. Herbal remedies for parasites also aren't going to work. There ARE some who maintain tanks and work on immunity or minimizing the impact, but those also require lots of work and otherwise pristine conditions and fish suitable to the environment. A blue tang, or powder brown, isn't suitable in a 90 gallon so they will already be a leg down (From build posts, you may have bigger and just didn't mention). They are ich magnets.
There are many variations on QT, but it still needs to be done and have medications on hand. Longer term observation, prophylactic treatment, or a mix, but it shouldn't go into your display. You already know the display likely has flukes, and "could" have other things. Those flukes will remain until all fish are removed and is left fallow, or the DT treated with praziquental. It's one of the FEW treatments that can usually be used in a DT. For ich, velvet, or brook if they exist you have going fallow left as the only option
And, I can attest, it's no fun
