I Managed to Killl One of the Most Indestructable Corals!!

I had 3 branches of a pink & white Xenia.  I had it nestled nicely in between the rocks and it grew for several weeks. Then one day, two of the branches withered up and died.  The third branch died the next day.  I'm not sure what happened.  The only thing I can think of is that the salinity level of the water dropped from 1.025 to 1.021.  My fault, I forgot to add the salt when I did a water change.  It is rather ironic that I managed to kill a coral that others have complained grows like a weed. Has anyone had a similar experience?