Lots of great suggestions,
Last I checked my nitrates were fine,
Never tested for copper
if I do have copper in my tank how do I get rid of it?
all my fish, hermit crab,mushroom and baby star seem to be doing great.
I think I will take a water sample to the lfs and test for everything possible.
Also I will move forward with the water changes every few days.

What do you use to filter your water for water changes?

I had copper contaminate my tank recently and kill half of my corals. All xenia melted in few hours and all my snails were just fine. The level of copper needed to kill xenia seem to be much lower than what is required to kill snails.

If it is copper, then use Seachem Cuprasorb to remove it and do water changes.

Anyway it is something to test.

I use an aquarium pharmeceuticals r/o unit. I keep a garbage can full of r/o water. The stuff usually sits for a few days before being used to top up, or water changes.

Ok went to the lfs.
Tested for
Nitrate
Nitrite
Ammonia
Copper
Phosphate
Calcium
Ph.
Ph and calcium levels where bang on.
No ammonia, nitrates or copper in the tank.
Slight levels of nitrite and phosphate.
Salinity was 1.027 tested with a refractometer.
Any thoughts, could it be the salinity?

def wold be better to have the salinity lower i prefer 23-25 but i doubt it was that that killed the corals .get the phosphate downs and youll see better coulors and im not sure if theres and algae in your tank but if so it will kill that too.

do you run carbon??:)

I've ran carbon for about 4 weeks. I didnt think the salinity would have been an issue, there isnt really any nuisance algae in my tank.
really dont know what the problem could be.

thats probably it too just a sudden shift to clean water from the carbon if i were you i would replace one of the dead corals and see if it dies off again:)