Sudden Coral Death in a Thriving Tank

by | Apr 8, 2011 | Corals | 8 comments

For those of you who do not know me, I have a 500G reef dominated by SPS corals that has been running, successfully by most standards, for the past 4 years.   Every night before I go to bed, I give my tanks a quick check.  Last night I checked the tank and all my corals were fine.  This morning when I checked the tank, one of my prized “Strawberry Shortcake Acropora” colonies had a huge white patch on it.  The tissue just flaked off overnight.   Half of the colony still has tissue on it.  Why did this happen?  All of the other corals are fine?  Is it time to panic with the fear that the “RTN” (rapid tissue necrosis) will spread rapidly throughout the tank?  Is this a random occurrence or the start of a pattern that something is about to go significantly wrong in my tank?   Should any corrective action be taken?  Typical dilemma when something goes wrong.

I am going to think aloud here and walk through my current thoughts.  It is a rather large colony of one of my prized corals. I really do not want to lose it; the first thing I am going to do is to cut a few fragments of it and plant them in a different location in the tank.  If possible I’ll move it to a different tank, but there I could run the risk of introducing some unknown pathogen if that was the cause.  But if I do not move it to a different tank it could RTN in the current tank since the conditions that it is exposed to have not changed.  Unfortunately, the same thing happened to a Lokani colony a week ago.  So now there are 2 occurrences of a similar event… start of a pattern or just 2 random occurrences?   Tough call to make, but if it is the start of a pattern the damage could be extensive.  At this point I am just going to not react quickly, try to save a few coral frags, and watch carefully.  Should I do a partial water change?  Or would that stress the corals out, making them more susceptible to whatever caused it in the first place ?

As you can see there is no easy call to make on this one.  Now the mind starts to run to assign a potential cause since it would point to a possible solution.  The water parameters check out O.K.  No drastic changes to the tank in the last month or so.  Ah.. must be the Bio Pellets that I added three months ago, or the fact I had skipped a water change while I was away on vacation, or the fact that I added 3 new fish yesterday.  But my engineering and statistics training has taught me – “Correlation does not imply causality.”  We are especially inclined to assign a cause to every problem without knowing if it is the action (or lack of action) that caused the event.  At this point I am going to just shrug my shoulders and let things go, especially since the cause is mostly likely undiagnosable.  Hopefully I will manage to save a few pieces of the coral and end up with more than one colony in the long run, or I will be knocking on the doors of my friends for a replacement.

  • Sanjay Joshi

    Sanjay Joshi in real life is a Professor of Industrial and Manufacturing Engineering at Penn State University. He has been a reef addict since 1992, and currently keeps several reef aquariums at home including a 500G SPS coral dominated reef. He also co-manages the 500G aquarium at Penn State. He has published several articles in magazines such as Marine Fish and Reef Annual, Aquarium Frontiers, Aquarium Fish, and Advanced Aquarist. In addition, he has been an invited speaker at several marine aquarium society meetings in the US and Europe. He received the MASNA award in 2006, for his contributions to the marine aquarium hobby.


  1. Cherrycorals

    Get out the band saw and gobs of superglue 😉

    Likely cause is not enough blue light…….

  2. phaedrus1

    Cherrycorals, what leads you to suggest a lack of blue light? Similar experience?
    I’ve had a red planet RTN for no apparent cause, however I had changed to 15K bulbs a short time before and noticed less polyp extension… then the RTN….

  3. James

    best 2 comments by far… wait, they seem to be the only comments! dammit.

  4. guarda2

    I had a .5″ purple nana frag go from deep rich coloring and great polyp extension to bone white overnight, over the course of no more than 6 hours. Every single sps piece in my tank (18 frags and mini colonies) looked excellent before and after. Nana never came back. Some people die unexpectedly and inexplicably in their sleep. Scientists worldwide continue baffled.

  5. ctxmonitor

    I would have to pinpoint it to the Bio Pellets, since for some reason there is a thread with sudden RTN, and in most cases they have the pellets in the system and they turn it off to correct it… Some had the pellets for months and months without any issue and then suddenly they just lose one sps after another. I would definitely take it offline, Sanjay..

  6. James

    I can’t speak for Sanjay but I am pretty sure he took them offline and is NOT a proponent of them. If I am right, I concur with him on that, it seems that you eventually hear horror stories from tanks running biopellets.


    test comment

  8. Sanjay Joshi

    I did remove the bio beads. Will see how well things stabilize. A few more corals have become victims of this sudden death. So I will be knocking on a few doors for the strawberry shortcake replacement 🙂


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