dead base on coral frag

[saltySamurai]

I'm concerned about the base of my green birdsnest - it's definitely dead. Is this normal? the other sps frags that I have are alive all the way down to where the frag meets the live rock. I don't see anything eating it, but... Will this spread or stop where it is? I noticed it about 2 weeks ago and have been watching it very carefully sinse - if it has progressed (not sure), then it's less than 1/8 inch in the last 2 weeks.


The color has shifted on the following picutre because I added a flashlight on the frag for more light. The first picure is more representative of the color.

 

[Mr. Wiggles]

It looks as though the upper portion has grown and now shades the lower areas from light and flow. I would say that this is a natural occurrence, although I would keep an eye on it to be sure that it isn't STN. I have a pocillopora mini colony with very densely pack branched, and the inside is generally dead looking. Best,

 

[saltySamurai]

I think this could have been caused by an alkalinity / pH problem I had for about a month that I think has since been cleared up. If the alk / pH / Ca are good and stable, will the good tissue reinhabit the dead area, or will it always be dead? If water is good, will any tissue loss continue up the and affect more tissue?