Help Identifying Sudden Coral Tissue Loss – Possible RTN or STN?

secomponent

New member
May 21, 2025
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Hey everyone,


I’m reaching out for help with a sudden issue in my mixed reef tank. Over the past 48 hours, I’ve noticed rapid tissue loss on a few SPS colonies — mainly Acropora and one Montipora digitata. The tissue is peeling off quickly from the base upwards, and some polyps look completely retracted or gone. No obvious pests that I can see, and water parameters have been mostly stable:


  • Temp: 78.2°F
  • Salinity: 1.025
  • Alk: 8.6 dKH
  • Ca: 430 ppm
  • Mg: 1340 ppm
  • Nitrates: ~5 ppm
  • Phosphates: 0.04 ppm

Flow and lighting haven’t changed recently. The only recent change was adding a new frag from a trusted local reefer (dipped, inspected, and quarantined).


Do you think this is RTN or STN? And what would be the best immediate step — fragging, iodine dip, blackout, or something else?


Appreciate any insight or experience from fellow reefers who’ve dealt with this!


Thanks in advance,
Jake ragdoll hit
 

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