STN in bird's nest

[d3rryc]

Hey, there!

I've got a small bird's nest colony (Seriatopora caliendrum) that started as two 1-1/2" frags about six months ago. In that time, they've at least tripled in size. However, over the last few weeks, they seem to have developed a form of STN. I thought at first that it was an allelopathy issue caused by a neighboring colony of yellow polyps that was encroaching on the bird's nest. I removed the polyp colony, but the STN not only has continued, but appears to be accelerating. I broke out the magnifying glass, and there's no sign of the dimpled look to the coral tissue that I'd expect from an AEFW outbreak, nor can I see any sign of red bugs. My chemistry has been stable, and the colony gets pretty decent flow from a nearby Koralia 2. Any advice?

Tank parameters:
Temp - 79
Ammonia/Nitrite/Nitrate - all zero
Phosphate - zero
pH - 8.3
Ca - 400
Alk - 9
Mg - 1350 (need to verify this one)

[apedroza]

Is the RTN in the bottom or center of the birdsnest?? It could be caused by overshadowing. Sometimes birdsnest get so big and dense that they can block out light to lower parts of the colony. I had one that was huge and grew rapidily but the base was dieing off.

[d3rryc]

It started kind of in the middle of the central branch. I've also seen full tissue withdrawal down to the white skeleton from a branch in full light, and I'm losing a big branch now that's not shaded at all.

[aquasport24]

start fragging the good branches ,before it kills the whole colony.

[d3rryc]

Just a quick update on this. I took Giau's advice and fragged off the healthy branches. I've still got a decent little colony to work with. There are three frags grouped together, each about 1-1/2" to 2", that should grow out pretty nicely. My working theory at the moment is that the colony of yellow polyps which used to be next to the bird's nest damaged it and allowed a bacterial infection of some sort to take hold. Everything else in the tank is fine, so I think I'm off the hook for AEFW or the like.