I'm not currently using my UTH as my thermostat died and the new one is on the way. Im maintaining the temps with just the che. The vet said everything was good in the tank to just keep him on paper towels for 2 weeks. The uth was turned off after I found the issue on his belly. So if it is getting worse I think I can say it's not a burn cuz he has no belly heat at the moment. The slide did show bacteria present. I'm told it will shed out but that could be another 4 weeks.
It looks like the area might be bigger. As you see in the picture there is well defined dark brown areas. Now at the end of that is a lighter brown general discoloration.