I have a good size hippo tang I got a few weeks ago that's been in QT. He had no parasites or issues when in got him but he developed a brown rash on one side. I thought it was heater burn, others mentioned maybe ammonia burns. That rash has started to eat into the side of him it seems, and I can't figure out what's going on. He was on copper and paraguard initially. The past week he's been on Mardel bacterial meds. He eats healthy and seems fine but it's driving me nuts and I refuse to put him in the DT. Ideas? Pic attached

