What usually causes RTN

[mfindell]

I have a Acro that was OK this morning and then started turning white at the base this evening. Cheooped her up and hope for the best. Is there a general rule for why this happens???

[TCU Reefer]

Tissue necrosis can be very mysterious as to what caused it. There is no one answer to your question. Usually, sudden changes in your system's equilibrium may contribute to RTN/STN. Swings in Alk, salinity, etc. may be the culprit but not guaranteed.

Chemical warfare from other corals may also be considered.

There's no one solid answer for this occurrence so just think about what changed since the last time the acro was healthy.