too be honest if your talking about that red bar that runs down his face it just looks like his natural markings to me. bettas can flush their colours depending on their mood. the fact that he may be a little stressed might be influencing his colouration. my female bettas flush quite noticeably when I feed them. my male is quite dark in colour so it isn't as noticeable. your fish is quite pale in comparison so I would imagine it would be more prominent. he would have to have been exposed to the ammonia for a while before burns developed on his skin. his gills would be red raw before any markings on the skin. his fins also look okay to me. he looks like a crown tail. the fins would melt away first as well. bettas are prone to fin rot. its usually the first indicator that they arnt happy.