Help Please ASAP

I have a RedTailedCat that looks like its been burned like 3rd degree burns all over its body covering 50% of it's body the skin is peeling off like a burn victim looks like bare meat with red out lines I'm working on pics as fast as possible other than the skin he's breathing a little heavyer than normal but not much and is swimming normal as well but this happened so fast it had a couple small marks on it yesterday But when I got to look at it to day it's unbelievable it looks like some one poured boiling water over him . my first guesses would be a flesh eating bacteria or a super fungi please any help would be great all I did so far is remove roommate pleco and did water change of 33% but the nitrate where not that bad 20 to 30 ppm now there below 15 ppm and I then added melifix for anti Bactria and some salt if its a fungi % 4 cups to a 125 gallon tank I put the salt in a cup to slow dissolve out hope the salt didn't burn to much on open wounds What should I do or not do Please help this is hitting him very fast and hard Also he is about 16 to 18in and I did water changes every 5 days

It's been setup and running for a year and there was no ammonia present just about 20 to 25 ppm nitrate no nitrites ? even if there was alot of ammonia aday or two ago to cause the burns there should be traces of nitrite left it all wouldn't be converted over by now not in the amount it would take to do this ? ????? what do you think

What the hell is this ????

This happened in 24 hours ??????????

A pleco about 30 to 45 days ago came out of my pond in WI but the pleco looks fine He was removed about 12 hours ago

Thanks for looking trying to get as many eyes on this as possible its moving very fast and he needs help please ask around and show others