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It sounds like RTN or STN to me. If you are new to SPS, it could be a water quality issue or acclimation issue. The only thing you can do to save it is to frag above the area where the RTN is happening; about 1/2". If you bought small frags, there probably isn't a lot you can save. /DesktopModules/ActiveForums/themes/_default/emoticons/sad.gif

 

From a quick web search....

RTN is rapid tissue necrosis. RTN is where an sps coral starts to flake tissue off the skeleton. This is contagious so it can spread to every sps coral in the system. It is from shocking the coral by any of the problems I listed above. Fragging the coral is sometimes the only effort available to save it. Sometimes that doesn't even work. RTN happens when all things are not stable. RTN happens from introducing an already affected coral too.

SDR is shutdown response. This is where an sps coral just fails to thrive. It can happen in frags or full colonies although after a colony is at a large enough size that is usually not the case. Frags can be growing and then just stop and go into decline to the point of either becoming a coral affected with RTN or just bleaching. The actual thing that is so highly debated about RTN is whether it is bacteria or a virus pathogen. Exactly what starts it is also a big debate but in Eric Borneman's book Aquarium Corals he covers it quite well.

STN is Slow Tissue Necrosis. The coral’s ’skin’ recession begins at the base, and ends with the axial corallites (tips). For now, the reasons are still ambiguous as there are many factors to consider. Some people claim that they see it begin with alkalinity swings. Some say that with temperature swings, you can get the same results. Currently, there is a new belief that in a low nutrient system (such as a Zeo, Ultralith), you can trigger an STN event.

 

I'm no expert....trust me on that !! Like I said with the previous post, I did a web search for those words. To me, those issues (regardless of the name) all have the same root causes: water conditions, stability, and nuttrition. So, to me, whether it's RTN, SDR, or STN...I'm not sure it matters what you want to "call" it. The solution for all is a stable system with good conditions; a state we all strive to achieve.

 

I talked to Tim last Friday when I was in Des Moines last Friday. Very impressive guy. I talked to him at length about tank flow. For fish-only tanks, 10 to 20x is acceptable and 20 to 40x for reef tanks - higher for SPS tanks. I just recently increased my flow to aobut 30x, but the problem is that it starts moving/blowing sand all over the place. So I've had to reposition the pumps to prevent so much sand movement. Anthony Calfo also talked about that at Frag Fest.

 

In my experience birdnest and pocillapora are both very susceptible to RTN. They tend to grow fast and dense and if they get to the point were it starts restricting flow to the base and/or inner section of the coral RTN becomes more and more likely.

Once they start to RTN the only solution is to frag it. The frags usually do fine as long as they are cut well above the dead area.

-JB