stn or bleaching? what to do?

[Hyperion1337]

Hi, I have had this blue tort frag for over 4 months now but recently, I've been noticing white spots in the center of the coral near the base. It hasnt been spreading quickly so i could rule out RTN but i was wondering whats going on? stn or bleaching and whats the next thing to do so that i do not lose the frag? My other sps corals like my montis, rp and aqua-green stag are not having any issues at all, they are actually extending their polyps to the max.

here are some pics:

the polyps are retracted b/c i cut off all pumps to take this pic. What is that white spot?

specs:
15 tank w/ dual t5ho over the tank
filtration:
diy HOB sump/fuge that has graci, caulerpa and mangroves
chemi-pure elite
modded biocube skimmer

ammonia: 0
Nitrite:0
Nitrate:undetectable
phos: undetectable
salinity: 1.025-.027

my tank has been set up for about a year now.

livestock:
pair soon to be mated clownfish
6 line wrasse : MIA

 

[Hyperion1337]

edit: I am also dosing B-ionic weekly.

 

[Acropolooza]

that is rtn

 

[Hyperion1337]

that is rtn

really? cuz if it was rtn my tort wouldve been gone by now its been like that for a while should i frag?

 

[Hyperion1337]

bump any help?

 

[Hyperion1337]

bump.

 

[dirtyBit]

Sorry to hear. I'm no expert but have you ruled out bugs? Also someone always says to check your Alk.

 

[ange062]

Hard to see anything in that pic. RTN and it would be gone in hours. If it's been a slow process as you stated (STN) one thing to look for is pests like AEFW or redbugs. Smooth skinned corals like yours are more susceptible to these IME.

 

[Hyperion1337]

its been like this for like a week or 2. I ran interceptor in the tank about 2 months ago and i havent added any new acros lately, so no redbugs nor aefw, i dipped in Rx.hmm havent checked my alk in while so i'll do that soon.

 

[samuelkl]

If you havent check alk in a while, then that seems likely. Torts are usually sensitive to alk changes