Sick ropefish, showing fin rot, clamped pectorals, lethargy, and red specked jaw.

Purchased two ropefish and two plecos. One ropefish is showing the symptoms mentioned in the title.
Upon inspection after a night in quarantine one ropefish was showing melting pectoral fins and barbells with some red pin point spotting around his lower jaw. Suspecting finrot/internal bacteria I started dosing with Kanaplex.

As of today, there is no improvement, with more reddening of his jaw, and a new area of rot on his tail, at the top.

I'm starting to lean towards costia maybe, should I start a formalin dip?

Also, if it is costia can rid ich plus be used as a dip instead of a bath?

Well, as of today it has progressed to his gill covers and a larger portion of his tail fin. Should I start Methylene blue dips? A different antibiotic? Euthanize?

Thanks Tom and Wailua.

I'm going to euthanize. It has progressed into his body by the tail, and the entirety of his soft gill plate tissue, and serious streaking has developed. He'll gulp and burp air, but there's little movement, and sluggish breathing. I hope it doesn't transfer to the other fish in QT with him. Seems ropefish are having a rough time at the distributors (my LFS has stopped ordering them due to Columnaris.)

Aquanero said:

The fish was showing signs of Septicemia and a possible secondary infection not Columnaris. The meth blue would have helped imprive breathing and the transfer of oxigen to the blood stream, the salt would have help fight the infection with the added benifit if improving gill function. If it started to show improvement I would have suggested adding Triple sulfa to the MB salt bath. It would have been worth a shot I'ne seen worse make it back.

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I wish that was true, during my trip to get clove oil it passed.

It was on its third day of Kanaplex, and second day of Kanaplex + Furan-2 mix. It had one Methylene blue + salt dip earlier today. Once it hit the body it had an offwhite coloration in a round shape, with red edges that spread 1/8th-1/4th an inch every 12 hours or so.

When it died, its entire tail had gone white and started flaking, and the infection had spread a good inch on its body, it was a cloudy color with a red edge. Both gill plates were dead, and folding back, with the same off white patch with red edges advancing up its face and belly, outward from his pectoral fins.

Sorry if that post came across as rude, losing fish always puts me in a poor mood. Thank you again for the suggestions and advice, it is greatly appreciated.