HELP!! What is this??!!

[Lilly123]

I just came home to my ranchu who has a red patch on her, but it doesn’t look like red pest disease. Is this a bruise or scratch? Please help, I’m very worried!!

 

[Chill]

What are your ammonia levels? My fish turned red when the ammonia levels got high. When I lowered the ammonia levels the red spots turned black