STN or Bleaching?

[MillerReef]

I have a TriColor Acropolis that has been thriving in my tank for 18 months. Recently, I noticed a white spot on the shaded side of the coral only. The spot has grown slowly but has remained only on the shaded side of the coral. I have included a picture of the shaded side of the coral with the white spot as well as a picture from the top of the tank of the side that gets light.

Does this look like STN or bleaching?

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[DivingTheWorld]

Looks like STN to me.

 

[shingo43]

Could it be possible you dosed something on it? Last time I have similar things because I added 2 park KH and it was blowed into the coral

 

[bobssecrtsn]

STN, For sure.

test for param. inspect for pest. any angels etc?

you are getting a decent P.E so I think its something bothering it. or pecking at it.

 

[MillerReef]

Temp: 77.2
PH: 8.1
Sal: 1.025

NO3: .75
PO4: 0.10

Alk: 3.0/8.4
Cal: 405
Mag: 1440


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[MillerReef]

Phosphates usually run .01-.05 so they are def higher than normal. You think that might be the cause? I threw some gfo in tonight to bring the level down. Hopefully it will help.

The thing that is strange is so far the white spot will only progress into shaded areas. It seems to stop progressing once it reaches direct light.

What I am trying to decide is how long to wait before cutting off the areas that are still unaffected. Any thoughts?


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