HELP! Monti digitata flesh "bubbling off"-- RTN??

[evilmantis]

I've had this monti in my tank for a long time. This morning I noticed that a substantial amount of flesh looks like it's bubbled up and detached from the skeleton. Is this RTN? I'm going to frag off the bad stuff, but it's a substantial amount and looks like it's spreading (some areas more detached than others).
The only changes I've made recently:
raising magnesium to battle bryopsis (about 1300 right now, raising about 25 per day)
brought up pH 0.1 per day because it was down at 8.0
Params:
nitrate/nitrite: 0
ammonia slightly elevated (makes sense since there's a piece of coral dying in the tank)
pH=8.25
salinity=1.028 (prefer to keep it around 1.026, so it's up a little)
alk=6.0 meq/L
I use RODI water. All other corals and fish look happy. So other than fragging and a water change what should I do? What could cause this?
Thanks
Goldie

 

[spanko]

Alk is high



Alkalinity (meq/L)
Natural Seawater Value: 2.5 meq/L (7 dKH)
Acceptable Range: 2.5 to 5.0 meq/L (7 - 14 dKH)
This can certainly cause RTN.

 

[nikesb]

i would not say thats RTN, ive seen this case a couple of times and someone suggested it was like cancer for SPS. just frag off that segment

 

[spanko]

IMO this
'I noticed that a substantial amount of flesh looks like it's bubbled up and detached from the skeleton."
Is the perfect description of a SPS coral RTN ing.

 

[nikesb]

at 7 dkh, it shouldnt cause that
http://www.reefcentral.org/forums/showthread.php?t=1253295
looks like its not something to worry about.
if the skeleton is completely showing, then you have a case of rtn. rtn usually happens within less than 5 hours