Montipora Self Destructed!

[canadawest]

Has anyone had this happen before??

Last night both of my Montipora Digitata (tan) frags were looking great. Both have been growing extremely well since I got them about two months ago.

This morning I awoke to quite a shock. One of the Montipora looked like it completely self destructed. All of it's white skeleton is visible, and a tan slime is covering the entire coral.

What the h&ll happened???

Has anyone else had a Montipora do this, and do you know the cause? I haven't added anything to the tank other than Kalkwasser and the occasional buffer, and that's been a regular routine for many months. All water parameters check out great.

The odd thing is, the other frag is doing excellent (as well as a tiny piece I broke off and am starting a new frag with), so I'm pretty confidant that it's not water chemistry related?

Thoughts?