A little help
 

So over the last week I have been siphoning out little red bugs. Flat worms are what I found them to be, and on sunday I did a dose of Flat worm exit. Man that stuff works as good as an H-bomb, As they were dieing I siphoned out the dead bodies and the cobweb looking things that they left behind. I watched carefully and after about 3 hours I noticed non of my coral were opening up so I proceeded to do a 30% water change and again watch. Monday I took the afternoon of to do a little more maint as I wanted the rest of these darn things out. When I went to bed last night everything was going fine. All fish were eating, the crabs and shrimp were doing their thing, corals and such looked good, but this morning I woke up to my Yellow tang dead. :(
Do you think it was from the flat worms? I am at work now so there is no way I can get home to do a water change or even checkon them.
I need some Ideas, anything that you think would help fix things or understand what I did wrong, or need to still do.

Did you run carbon?

Maybe the stress of everthing just caught up with him? How do the rest of the fish look?

Yes and I still am running carbon, it will be removed tonight.

Everyone else looks fine, as of this morning, haven't checked them since.
When I went to bed last night everything/one was fine

Everyone looked good lastnight and this morning. Stress from something I guess, if it was poisoned I would think other things would have died with it.

Some fish are definitely more resilient than others, and I've found the yellow tangs to be less resilient than most. Just my own personal experience.