If by turning gray you mean that there is a gray like matter overtaking them and if you remove them it smells spoiled then they are melting away. Sometimes this happens to zoanthus. You can possibly save them by placing them in front of a powerhead in a bucket of tank water and blow off the gray crap. Then dip the zoas in a solution of iodine that is intended for reef tank use, you can get a coral dip from your local fish store.
This might save them, maybe most of them, but even a few is better than nothing.
If there are some good polyps left now, it might be best to frag them off and get them away from the infection, cut at least 2-3 polyps away from the gray. The infected polyps you can try to save with the powerhead/bucket/coral dip.
