My xenia is turning black

[Slick]

So i just did a water change and now some of the polyps of my xenia are turning black and they don't look feathery anymore. They still pulse, but not as much as before. Is this normal? I might add that i just used some bSi IC-GEL to glue a rock down in my tank b/c i was told that i could use this glue under water.
Slick

 

[RGibson]

Do a water test ,when xenia are not looking good it is a sign that the water is not right.