3 spot angelfish Hiding

[silversides]

I have a 3 spot angel for about 1 year, the tank (125g) has been set up for two years. The angel has been a great fish alwas swiming around and would come to you at feeding time.Now for the last 6 days it stays hidden under the rocks and will not come out. all water conditions are still good. It still looks healthy with no marks or spots and does not act like it's sick.
The other fish and coral are acting normal.
Any ideas?

 

[silversides]

I added some colt coral and a feather duster but the angel did not go into hiding until about 15 days after i added them. I did a 25 % water change with no results and nothing else looks abnormal. I have not seen the angel feed.
Thanks for the ideas.