patchy necrosis

[kangarooman]

Hey:
I have been having an unusual situation occur with one of my acroporas in the past 3 months or so. Approximately every 2-3 weeks, a few small areas of the colony (acropora valida i think) detissues. It appears almost like paint cracking on a moving surface (a reticualted pattern). After a few days, the healthy surrounding tissue regrows and covers the skeleton, but the about 2 or 3 weeks later, the same thing occurs again. It has never affected the other acros in my system, and never escalates beyong a few small areas on the base of this stand, but baffles me nonetheless. Any ideas?

[KillBill75]

Possibly Shedding?

[kangarooman]

Well, I don't think it's so much shedding, becasue it is not a mucous release, but instead the live tissue, exposing the white skeleton underneath. Quite honestly, I've never seen the actually tissue sloughing, I've just seen the white skeleton exposed. Also, I have seen the healthy sections shedding the mucous.
Ive recently increased my salionity slightly, as I had it down to about 1.021, but I can't imagine that would be effecting it in such a localized way.