What is going on?! Montipora bleached overnight?

[Pwnm30rdi3]

Hi folks,

This red montipora has been growing in my tank for about 13 months from a frag. I woke-up this morning to find that nearly 30% of the montipora had bleached overnight.
I haven't changed much in the last few days. Yesterday, I added a new bag of Chemi-clean Blue. (In hopes to remove any toxins from the minor Cyano / Diatom bloom I am battling)
I added 60lbs of dry (thoroughly rinsed) sand to the tank about 8 weeks ago. The only problems from the added sand have been Diatoms and Cyano eating up all the silicates.

Params:
Alk - 8.2 (Alkatronic)
Calcium - 445 (Hanna)
Nitrates - 4.30ppm (Hanna LR)
Phosphates - .06ppm (Hanna ULR)
PH - 7.95 - 8.2
Temp - 76.6 - 78

 

[PanchoG]

The seems odd to me, I can only wander what about Mg, do you have test result?

 

[Pwnm30rdi3]

The seems odd to me, I can only wander what about Mg, do you have test result?

It took me by surprise also. I did mix up a new batch of Sodium Nitrate recently. I have a low bioload, I often dose a few mL of NaNO3 each day. Maybe this batch was contaminated? It was sold as reagent grade.

My Mg test kit expired in 2018. Turns out I don't test that one too often. I'll grab a new test kit and report back.
I expect it to be normal-ish. I rely on my DOS to do continuous water changes to replenish trace elements.
Salinity looks normal, 1.026.

 

[Pwnm30rdi3]

So far, my Acropora frags have not bleached. Fingers crossed.

 

[PanchoG]

It took me by surprise also. I did mix up a new batch of Sodium Nitrate recently. I have a low bioload, I often dose a few mL of NaNO3 each day. Maybe this batch was contaminated? It was sold as reagent grade.

My Mg test kit expired in 2018. Turns out I don't test that one too often. I'll grab a new test kit and report back.
I expect it to be normal-ish. I rely on my DOS to do continuous water changes to replenish trace elements.
Salinity looks normal, 1.026.

I don’t think your NaNO3 is the reason, all the corals would be affected. The Mg would be one reason, have you checked your lights in that side of the tank or stray currents?

 

[Pwnm30rdi3]

I don’t think your NaNO3 is the reason, all the corals would be affected. The Mg would be one reason, have you checked your lights in that side of the tank or stray currents?

Lighting looks good, checked this morning.
I'll test for stray current today!

 

[Pwnm30rdi3]

No stray current detected by the multi-meter. I went ahead and bought a grounding probe anyways.

I also purchased an Innovative Marine Helio Heater to help stabilize my temps even further. The tank temp seems to stay within .4 degrees of the target at all times now. My old Eheim JAGER heater would swing up to 2 degrees in either direction over a period of 12-24 hours.

Magnesium test kit should arrive today.

I haven't seen additional bleaching, but the Montipora has not yet made a recovery either.

 

[TX_Punisher]

Did something settle on it like salt creep falling off a net cover?