The white area looks like it's newly exposed, I was thinking it was cut when it was fragged. Decay would be brown and slime looking on the fleshy parts. If it was a poor frag job (no offense to whoever did it, it happens to the best of us) the pieces could just be falling apart which isn't a concern since any head will live independently. If it's a coral you've had a while the heads do naturally separate as they grow to have more room. As far as not extending goes, if all your normal parameters are stable I wouldn't worry too much since they do go through points of beeing more or less extended as they grow. If it's completely retracted for more than a day (the entire head) and all your paramataters remain stable, at that point I'd do a dip in what ever antibacterial (iodine type) solution you choose just to rule out bacteria etc.
If your going to move it for more light I'd try a very small move. Maybe do one head where it is and the other out of the under croping to see which one seems happier that way you can compair and make a decision.
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