Welcome to Reef2Reef!
Sorry for the delay, I missed your post and just saw it now.
The spot above the pelvic fin isn't a fluke, it looks like it is either a fungal or bacterial plaque. How long has it had it? What I see that concerns me more is the general blotchy coloration of the fish's body and slight cloudiness to the pectoral fins - THAT indicates flukes to me. Emperor angels get Neobenedenia flukes pretty often, a 3 minute FW dip isn't going to dislodge those, you need to go for a full five minutes and then check the bottom of the dip container for things that look like scales falling off...and that isn't a treatment, just a diagnostic tool.
Jay