Damn... Thanks guys..

It's not really a new addition, and the MH has been on the tank for awhile now.. Perhaps the photo period is too long too..

I'll try moving it to the bottom... See how it goes for a week. :neutral:

You can try that but it also can be water quality or stability. In my tank I am battling Alk swings. I loose a piece about once every two weeks. Starts the same way as yours. Ive have stopped a few pieces from fully dieing but don't know what I did other then get the Alk back to around 9 DKH. The best thing you can do for SPS is keep your water as stable as you can.

Chris

I think its toast... i went out for a couple hours, and came home to see half the colony has gone completely white...

That is STN...RTN is much faster(minutes to hours). I have a piece that did that slowly. In fact I tried to frag it and move to another tank. Still went on me. This coral was was probably streessed/infected with something. This STN was random...didn't happen to nearby corals. I have only seen one case of bleaching. The difference is that you can actually see poylps.

That's too bad. If you ever see this again, it requires painful, immediate intervention. As others have said, frag mercilessly. You want to remove pieces that are completely away from the dying area. Usually, I'll dip the frags in an iodine before mounting them somewhere else.

I have also experienced that one coral dying in this way, can lead to a catastrophic, massive die off of every coral. I have a theory about this, which I won't get into, but dead/dying pieces should be removed from the system as soon as you see it.

Thanks! ^^

It's out of the tank now... I can't believe how fast it spread while I was out. Hopefully I got it out quick enough that I don't loose anything else..

I would also do a dip to check for parasites, Acro eating flat worms often consume a coral slowly,