colt coral.

the last few days i have noticed my colt coral has been shrinking, almost as if the lights are out, polyps are extended but it just doesnt look right.
I have done all my water test and everything checked out although im sure i have a phosphate issue since there is some cyano in my sand im trying to deal with.
all other corals are unaffected and i wasnt sure if the colt does the same as some of the other leathers and go through  a shed.  this was one of my very first coral and it just seems odd for it to suddenly start acting wierd.  any thoughts or ideas what  could be going on? or perhaps i should consider removing it? although it is firmly attacked to a rather large rock