A little info on RTN....
RTN (Rapid Tissue Necrosis)
Though sometimes referred to as if it were a disease, RTN is not a disease. It is only what its name implies, rapid tissue death. This is when, for any variety of reasons, a coral's tissue begins to rapidly die off (usually leaving the entire coral dead within a few days if not a few hours). Once it starts, RTN is nearly impossible to stop, especially when the cause is unknown. Sometimes a sudden and drastic shift in tank parameters (such as temperature, salinity, pH, etc...) can cause RTN.
<span style="font-size: 12px">IMMEDIATELY remove any coral you suspect to be suffering from RTN. Though it's not known what causes RTN, it has been shown to spread to other corals. This could be because it is caused by an infectious agent. Or, it could be that when one coral dies so rapidly, a significant amount of toxic chemicals are released into the water causing other corals to start dying (a kind of chain reaction).
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Starvation
<span style="font-size: 12px">Unfortunately, many aquarists do not properly feed their corals. Slow tissues recession/death is often a sign of starvation. If you suspect that your coral is starving, please see http://www.asira.org/caresheets">Coral Care</a> for information on feeding your particular coral. </span>
[B]Stress[/B]
Most corals, particularly wild caught colonies, suffer considerable stress before arriving at your local aquarium store and into your tanks. Inappropriate and/or highly unstable tank parameters, excessive handling/falling/moving, and unfriendly tank neighbors are some common causes of stress. Stress can lead to slower tissue recession, poor polyp expansion, slowed growth or just an overall decline in coral health. When severe, stress can cause RTN.
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