We need a bit more history about the tank and fish. Here is a link:
Aquarium Fish Disease Problem Solving Determining the best course of action for a problem with your aquarium can be a difficult task. Even advanced aquarists will often need to seek the help of others for complicated or unique issues. Our intent here on Reef 2 Reef is to offer expert advice...
www.reef2reef.com
As said, flukes do not show as white spots. However, in looking at your photos, I see spots of vastly different sizes, some are pretty large. Ich doesn't have that much variation. However, sometimes poor focus in these photos gives the illusion of different sizes, so I'm not ruling out ich right now, but you should consider that these could be idiopathic mucus plugs, something that blue tangs do in response to stress.
The best way to tell the mucus from ich is to take a photo of the fish and then take a second photo, from the same vantage point, 24 to 36 hours later. If the spots are essentially in the same location, it is most likely mucus. If the spots have mostly change location, and changed in number (both decrease of increase) then it is more likely ich.
Jay Hemdal