pollups dissapearing!

[jja]

I have had a large group of green polyps that I have had for about 2 years and all of a sudden there is a patch about 4 inches that is just gone. Just white rock underneath where they used to be. The only new additions to the tank are an arrow crab and a blue regal tang. Any ideas?

 

[full of questions]

Do you see them any where else in the tank? It"s normal for
polyp"s to do this.

 

[powdertoastman]

have you got any new rock as of late? maybe you have a bad hitch hicker that is eating them? just a thought.