Fin rot.. I think?

I adopted 6 guppies 5 days ago, when I got them home I realized that a couple had fin rot or had been nibbled on. I immediately started treating with Herbtana and Artemiss from Microbe-lift. All but one of the affected guppies has gotten better, and this one seems to be continually getting worse. This morning I realized that it has started to affect the back side of his body. Is this actually fin rot? At this point, do you think he would recover or should I euthanize him? I have kept fish many times, and never have had to put down a fish. In this circumstance I think I might have to for his own good, but I just want to know first that he will not recover before I decide to do so.

Has anyone had a fish this far gone recover?

I had a betta lose almost all of its fine. I did lots of water changes, added small amounts of aquarium salt and the did a treatment of jungle fungus clear (think that's what it was called.) He is super sensitive now If i miss a water change and it came back a couple times but is doing fine now

Juice, thanks for the response.

We have a few shrimp in the tank, so we can't add aquarium salt or anything with copper I've been changing the water every other day.

Does this look like typical fin rot to you? I know It can spread to the body, just never seen it do this.

I have used salt in a shrimp (RCS) tank, no ill effects.

Thank you both for input, yesterday morning he was being picked at by a shrimp. Didn't make it

Everybody else in the tank is happy and healthy, still thriving. I'll continue using the treatments of Herbtana alternating with Artemiss until the 10-day period is over, just to make sure nobody else gets sick.

Naughts said:

I have used salt in a shrimp (RCS) tank, no ill effects.

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Really!? I thought they were really sensitive to salt? What brand and how much in a what size tank? I'm very curious now!

25 litre red cherry shrimp tank had hydra. Advised on here (Big thanks Colin_T) to use 2-4 tablespoons aquarium salt (API) per 5 gallons. Used 2.5 spoons dissolved and added a bit at a time over an hour. Left for a week. Did 10% daily water change for a week to slowly reduce salinity. Then returned to routine weekly water changes. Voila! No hydra, shrimps fine.