Is this a sign of STN?

[mastawong]

I just lost an SPS colony a few days ago due to RTN, according to the LFS, I had an alkalinity spike, my alk went from the usual 11 to 12.6 in 1 night, and my calc went from 420 to 300. Not sure what caused this, anybody has any ideas?
Today I noticed my alien eye chalice is starting to turn white for some reason, my current water params are:
Temp:81
Calc: API : 340, Salifert : 420
Alk: Tetra : 9-10, Salifert : 10.6
Ammonia/Nitrite/Nitrate: 0/0/5
Magnesium: 1200 -> dosing 10ml of magnesion right now
PH: API:8.0-8.2, Salifert:8.0
SG: 1.025 - refractometer
Tank is 20g w/ 4g fuge.

Here's a pic:

 

[benihana]

how long have you had the Chalice for?

 

[mastawong]

about 1 week, should I cut off the white area?

 

[DetectiveTofu]

When you placed it into your tank, was that portion of flesh gone? Or did it recently just start happening?

 

[650-IS350]

You might wanna get your mag to 1300-1500

 

[seapug]

I don't think that's STN. STN/RTN is usually much more dramatic (rapid peeling/dissolving). The shape of it is very "square" so it looks like a bruise from some sort of physical contact. I'd just keep an eye on it and avoid futzing with it any more than necessary.

 

[mastawong]

Well it did spread out a little, so I chipped the white part off. I'm slowly dosing mag now.

 

[Bebo77]

are those constant water parameters? how much does your alk fluctuate

 

[mastawong]

I don't test my alk during the day, only at night, so I'm not sure how much my alk fluctuate. But I tested my alk this morning using tetra test, and I got 10-11dKH.
My bubblegum chalice is browning out, and it's placed close to the alien eye. All other corals look fine though, so I'm guessing they're getting too much light, they're placed about 12-13" almost directly under a 150w MH