help me save this poor guy with damaged fin

Hi,
I received a few wild discus last week and this guy arrived with an injured fin; I am not 100% sure if this is an injury or an infection but certainly does not look good. The injury is over days getting more swollen and he is becoming more shy and dark. So this is not getting better but slowly getting worse.
What would you recommend to do? Quarantine and treat with anything?

Here are 2 pisc a few days after arrival:
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here are two more pics today - another ~5days or so later so you can see the fin is getting more swollen:
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Looks like this. https://edis.ifas.ufl.edu/publication/fa181

The link seems to be dead but when I googled this fa181 publication I saw other references pointing to it suggesting this might be Lymphocystis?
Assuming this is what you are suggesting, probably there won't be any use in quarantining with no treatment options...? Would it make sense to isolate it anyway to prevent the spread of the virus to other discus in the tank (there are 12 adult wilds in there)? ...All others perfectly healthy at the moment.

That’s what I’d do. Put it by itself and add salt to the tank. Can’t hurt. Change water daily. Last thing you want is it infecting the others.

I've seen something like this before and it didn't turn out well. If this is viral then I would isolate the fish and treat with a gram positive/negative antibiotic to eliminate any bacterial or secondary infection, and salt at about 4-5TBS per 10g. Regular large water changes and replace the salt removed during water change. Let it run its course and see what happens, or after the antibiotics you can try a high heat treatment. I doubt you can get the heat high enough to kill the virus and not the fish but it may be worth a shot...

Brian, do you think that lowering the pH would help? I've never tried that myself but I've read about it.

It certainly wouldn't hurt as long as he doesn't have a ph crash, but if this is a virus then it's internal so I'm not sure how effective it would be. I've also read that raising the ph can effect certain cancer cells and viruses but unfortunately it would probably kill the fish as well. I just don't know that much about viral conditions in aquariums. That's assuming this is a virus at all. Reducing the chance of bacteria or secondary infections is the first step in either case.

I've seen this in a fish I had some years ago. Never did heal. Antibiotics won't work on a virus if that is Lymphocystis, which it seems to be by looking at the pics. But the fish did get a secondary septicemia infection as time went on. I eventually put the fish down.

I know antibiotic won't affect the virus. I was concerned about secondary infections... I've seen this as well and I agree with the prognosis...

Here is a better look. https://discusrescue.com/lymphocysti...ase-treatment/

Quick update and a request for advice: I received feedback also from the supplier / importer (Santarem Discus) who suggested I should treat him with Sera Bactopur Direct - this is a broad spectrum antibiotic. Although it would not kill the virus it would prevent bacterial infection which in their opinion is also causing the "cauliflower" swelling... It probably makes sense, but as I am watching the fish today he is in a much better mood and colourful again... not sure if taking him out to a quarantine tank and dosing him with antibiotics might only make it worse? But as he is such an amazing fish, I definitely want to do as much as I can to stop this illness and bring it under control. I am setting up the quarantine tank now, but what would be your opinion - to do this or not? I leave for a business trip in a couple of days so will not be able to change then... he will either undergo a week-long antibiotic treatment in quarantine tank or a week will pass with him being with the rest of the fish and we'll see what happens...?

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He does look better but I would still put him in QT so he doesn't spread the virus to the other fish. I'm glad that Santarem is helping you. They never should have shipped that fish despite how beautiful until they had treated and cured him. Wild Discus are expensive. No supplier should ever ship a sick fish.