RTN progression

[MikeG]

I have a blue tipped Acropora Formosa that seems to be receeding near the base of the coral. There is a ring about 1/2" thick that has turned white at the outer edge. It doesn't seem like the tissue has come off looks more like bleaching but it hasn't progressed in about a week. Is RTN always a rapid process or can it be slow over weeks.

This coral was introduced about 2 weeks ago and started to see this 4-5 days after introduction. Should I just see how it progresses or frag it and remove affected area?

Tank parameters are good
Ph 8.2, temp 78, SG 1.025, Alk 3.5 meq/L, Calc 425 ppm
Amm, nitrite, and nitrate are 0

 

[NateHanson]

Sometimes larger colonies will suffer STN (slow tissue necrosis) from the base up as they shadow their own base. Is this a big colony?

Another possibility could be red-bugs. I think I remember that some people were getting STN with undetected red-bug infestations. It's worth a look anyways.

Could also be that it got a little shocked in transport or acclimation, and if its not progressing now, and there are no stressors that I mentioned above, then perhaps it will color back up, or recolonize it's base.

Those are my moderately inexperienced guesses.

 

[MikeG]

It is not a very large colony, there are about 6-7 branches that are pretty thin but about 5" long. The base is about 2-3" across but isn't shaded at all. I have looked at it closely to look for any parasites but didn't see any. How difficult are the red bugs to spot? I was hoping that this was just from acclimation and it won't progress.

 

[Chuck Spyropulos]

Stn, Rtn

I have found that RTN and also STN is exacerbated by large fluctuations in Alkalinity, specifically large Alkalinity drops. On the other hand, sometimes it is hard to find an explanation. Red Bugs, parasitic flatworms, low or swift changes in alkalinity, temperature spikes, are other things to look at.

It is not a very large colony, there are about 6-7 branches that are pretty thin but about 5" long. The base is about 2-3" across but isn't shaded at all. I have looked at it closely to look for any parasites but didn't see any. How difficult are the red bugs to spot? I was hoping that this was just from acclimation and it won't progress.

 

[NateHanson]

How difficult are the red bugs to spot?

They can be very difficult to spot if you don't know what you're looking for. I got a frag with the bugs on them from an experienced reefer, and told him he might have the bugs. He checked and said "nope, don't see any". I urged him to check again, and he had a couple experienced friends look for him too. "nope, none there". Then a week or so later he told me he did indeed have them on a number of his colonies, and he just hadn't known what to look for. They're extremely small, but can be seen with a magnifying glass. Look for small spots that move. They're about 1/4 the size of a closed up acropora polyp, and have a pink or reddish dot on their back. Sort of comma shaped. You likely won't find them with your naked eye until you're familiar with what you're looking for.

By all this, I don't mean to suggest that I think you've got them. Just trying to tell you and others how to look for them. They're much smaller than I had originally thought.

 

[MikeG]

Thanks, I will take a closer look.