No I understand, and do appreciate the feedback and recommendations. It's quite the scary thing to deal with, so tips from the experts are incredibly helpful.
My current thought (and please tell me if this seems misguided) is if the new addition remains active, calm, eating, essentially acting "healthy" in all the other aspects bar ich, I'm thinking I bite the bullet on a hefty UV sterilizer and take all the previously mentioned measures- vitamin enriching their frozen foods, feeding well, keeping nutrients low / generally keeping extra close tabs on water, assuring there is no aggression, etc.
But I figure if that particular fish's condition declines and/or I start to see ich breaking out and starting to affect other fish, then I pull however many I can, go ahead any buy a treatment tank with separate everything, treat the struggling fish, and still stick a big UV on the back + take the mitigating treatments above. I just realistically don't think I can get everything out without totally destroying the tank (my little Biota mandarin will be next to impossible to catch unless the glued and encrusted scape is fully torn apart).
So based on some of the advice here, this seems like a decent plan, albeit not perfectly kosher. But regardless it's going to undoubtedly command a hefty price for the UV- no more coral budget for awhile, lol.
Does anyone have a recommendation for a good UV sterilizer + pump fitted for an 80 gallon system (reefer 300XL) that could do the job? It would probably have to be mounted to the back of the tank, but I have several inches between the tank and the wall. I saw
@Tamberav recommended a Lifeguard 55w, if this is the best option is there a standard pump that would fit the flow needs properly?
Thanks again everyone for all the help here. Glad I'm avoiding a money trap in that tiny UV