That stinks... Sorry. Does the red look like a fight mark or a bacteria or fungus?
What else is in the tank?
Male bristlenose female bristlenose and 6 fancy goldfish and some ghost shrimp.
Hm..it would be weird for a BN to do that..I could maybe see a bulldog pleco or something. I guess it could happen? Maybe he died..got sucked up by intake and floated back down? Idk what kind of filter you have..just an idea..