Don't use Ich-X, it isn't reef safe and is of no real benefit for marine ich or flukes.
The video shows rapid breathing in all fish, and congested skin and cloudy eyes in the tangs. That shows there are at least two issues going on here - possible protozoans (rapid breathing) and flukes (cloudy skin and eyes). The mucus feces is another issue, and one that may or may not need treatment.
Your best option would be coppersafe and praziquantel in a stable treatment tank. However, that is a best-case scenario and requires that you have an operational biofilter in your treatment tank.