SPS greying out

[magikfly]

I've been worried about a few SPS greying out. Not STN/RTN, they simply turn grey and stay that way. This has only affected 3 corals until now. The rest are doing fine.
I've only seen this happen in the wild and never in a reef tank.
My N is chronically low so I increased my ATI Nutritions N dosing substantially. No joy
Has anyone dealt successfully with this problem?
Tank param's
Reefer 425 (100g)
PO4 : 0.06
NO3: 1-2
K : 400
KH : 7-8 (in line with TMPro)

 

[T-J]

Looks like tissue loss from the pic, but you say it isn't?
Any chance it's getting shaded by the Monti next to it?

 

[magikfly]

Well, in the end the corals end up just as dead. It's just that it's not regular STN/RTN where the tissue lets go of the skeleton. In my case everything just shrivels up, dies and ends up looking like marine mummies. The monti does not shade and even if it did, I'd be looking at healthy albeit white tissue.

 

[TX_Punisher]

Did the no3 rise with the “ATI nutritions?” If not, try sodium nitrate. The Planted Tank (website) has a calculator that will get you close to start dosing

Have you performed an ICP type of test to look for any contamination?

 

[Saltyreef]

IME the grey comes after the tissue loss....

 

[driftin]

Have you performed an ICP type of test to look for any contamination?

I was going to ask this too. I had some corals go grey and then start STN, I found I had high TDS coming out of the RODI. Changed that and massive water changes, everything reversed except for one or two pieces that were too far gone.

 

[magikfly]

Good point, totally forgot I have that option.