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Mysterious case of RTN?

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After a week away from my reef I came back to find my blue milliepora colony and 2 out of three frags completely RTN'd. What is very strange is that everything else in the tank including my SPS look fine. What is even stranger is that the one frag that did not RTN was actually shaded by a larger frag that I had on the frag rack with it.  So What the HECK happened? 


As soon as I saw the ghost white skeleton of my beloved quick growing millie colony I started testing and testing again here are the parameters that I came up with.


ALK - 8.1

Ca - 385 

MG - 1440

SG - Between 1.026 and 1.028 ( It was higher before I left and I was slowly bringing it down) 

Ph - 8.1 during the day, 7.8 at night


Since I have just made the jump to dosing Two part these were the only params I tested, all other LPS, softies, Clam, and Nems look fine too. 


There were a few things that I am thinking could have been the cause of the RTN

1. Problems with Two part, since I just made the switch i might have upped the dose too much too quick, However all the other SPS are fine.

2. Salinity problem, My salinity was pretty high at between slightly above 36ppt, I use a DP-3 for auto WC's when I am gone and set it up to slowly put in 32ppt water, when I got back it was right at 34 ppt, again everything else looks fine.

3. I upped my light intensity, on my AI prime, I upped my RB channel mostly but also just bumped everything up a bit, total intensity only went from 31w to 33w 

4. Flow for circulation I am using the Innovative marine mightyjet (500) gph one, and have a MP-10. I had the MP-10 at about 85% set for the short pulse mode, I have been using pulse mode for over 3 months on this tank but I had bumped up the power from around 60% to the 85% about 3 weeks ago. Again everything else is fine, I have a green slimer that is pretty much directly infront of the MP-10 and is looking great. 


Can anyone weigh in here or knows if millies are super sensitive to anything? the other SPS I have are green and red cap, red setosa, green slimer, unknown blue tort, Pink lemonade, and a purple encrusting monti. I am utterly surprised that no other SPS in my tank RTN'd just the mother colony and the two frags. It is even weirder that the only frag that did not RTN was shaded  

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Perhaps all the combined changes.


How is your nitrate and po4?


It's not particularly unusual to have something RTN and others look great.


If you over did 2part that could certainly be an issue but sounds like the tank didn't have much stability as of late.

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There is research showing that some rtn is actually caused by philaster parasite. They decimate a coral in a day to a few days.


The parasite come about when a coral isn't healthy. 



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Could just be alkalinity swings.  Current levels don't tell us the whole story.  What were previous levels, and what are the levels of a freshly mixed batch of saltwater?  Specific gravity swings also swing parameters (by concentrating and diluting elements).

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