PH= ok is that with the lights on or off (run before the lights come on and after they have been on for awhile ) you may be having a swing
Ammonia = sounds like a bit of a cycle have you added any new live rock to the tank
NitrIte = is good
NitrAte = is good but to further bring down try chemi -pure it goes in the filter , what kind of filter are you running ? How often do you wash/change the filter pads
Temp = is good make sure there are no big swings in temp
Salinity = need to get that checked maybe low or high that could be causing the deaths or retraction
What size tank do you have , is it one 24 watt or 2 24 watt bulbs ,the lights may have reached the end of their useful life, and need changed
how much water are you changing in a week 10 %-20% week is good .
As for xenia I never could keep that here some people just cant keep xenia
as for the candy cane you may want to check the calcium levels and iodine levels . Hopefully others will be able to help you out more than I can