Montipora Digitata and RTN

I had a frag of M. Digitata and it was growing great and then yesterday I noticed at the base of it, that the skeleton was showing...I thought nothing of it at the time, because it was under a piece of M. Cap and was not getting light anymore... Today however is a different story. It is now completely bare and a white skeleton... I think they call this RTN? I wonder why it just affected it and not the other corals? Is there a primary cause for RTN in an aquarium? hmmm I am going to do some more research tonight and also a complete water test to make sure the levels are ok.... will post more later tonight....Thanks in advance for any knowledge you can add to this phenomena..

[reefrunner69]

Is there a primary cause for RTN in an aquarium?

RTN is a generic term, there are many pathogens that can cause RTN. This is the reason it is so difficult to treat, it's RTN, but is it caused by a bacteria that responds to a reefsafe antibiotic? Is it protozoan? Is it viral? Yes and yes and yes, depends on what is destroying your coral.

I wonder why it just affected it and not the other corals?

IME, RTN will only effect stressed, weak or damaged corals. It is contagious and the corals in your tank may be weak enough to succumb so it is wise to remove the coral, but it can be a one coral thing with no spreading.

Well, I just tested the water and hmmm...

NH3 = 0
NO2 = 0
NO3 = 5 meg/L
PO4 = 1 meg/L
ALK = 12.2 dKH or 4.32 meg/L
CA = 500
ph = 8.2

I am noticing the Xenia shrivling away also now...

I know the PO4 is high... Could this cause problems other than algae fuel? I know all corals need some, but not that much, but is it high enough to cause stress?

[reefrunner69]

if the level is 1 mg/l then yes that is very high, possibly high enough to prevent the calcification in your stoney coral, I don't know what other effects it might have.

Thanks