It's a judgement call, but the tomini may have flukes. It could also be ich - blanching around ich trophonts does happen (more so on other species like emperor angels). Normally, tangs with ich show the typical white, salt sized trophonts with no "halo" of blanching around each spot. Trouble is, the treatment is different for either issue. With ich, there is more often changes in the number of spots - the number of spots will wax and wane and change location over time (days). With flukes, the spots will stay in the same location over a few days.
Sorry to not have a more definitive diagnosis for you.
For ich, you would likely need to isolate the fish (and others probably) to a treatment tank and dose with copper, hyposalinity or chloroquine. For flukes, you could try Prazipro twice, dosed 8 days apart, with good aeration. The Prazipro can be dosed in the display tank itself.
Jay