LPS Die off - cant find a problem

[Sequest]

Tank is 2 years old. I recently lost a blenny to a suspected bacterial issue. The coral issues were seen roughly around the same time I noticed the Blenny was sick. Tank has not had anything new added to it or done to it in 6 months.

Calcium: 420
Phosphate: 0.012
Nitrate: 6.2
dKH: 8.6
Magnesium: 1260

The coral's look almost happy, until the head/area dies off suddenly.
Not all corals are affected, but it looks like it is slowly spreading like the plague.
Also interesting - its affecting corals down the bottom of the tank. Those up top have no issues (yet). Up top are some hammers, two goni's and an acro, all of which are happy.

I have taken these corals out, dipped them with Red Sea DipX, iodine and two of them with hydrogen peroxide.
I have also reduced my tank temp from 25.5 down to 24 (aiming for) as that was one bit of advice from Triton, although i dont think it has helped at all.
I have performed a 80% water change.
I have checked all my gear, make sure there is no obvious rusting, or items in the tank that shouldnt be there. Cant find anything.
None of it has helped.

Submitted an ICP and NDOC. Both came back with everything in the green, no heavy metals. The only thing of note is Iodine is a bit low.
NDOC told me not much.
Triton's "Help" section for my ICP simply says to contact them.

ICP results: https://www.triton-lab.de/en/showroom/icp-oes/219758
NDOC results: https://www.triton-lab.de/en/showroom/n-doc/12330

Any suggestions? I am running out of ideas and slowly watching my coral die.

 

[crazyfishmom]

Sounds like there might be a critter on the sand bed that’s nipping or something like that. Not sure what it would be though. Any chance you can pull them off the sanded and onto some of the rock a little higher to see if that stops the progression?

 

[Sequest]

Sounds like there might be a critter on the sand bed that’s nipping or something like that. Not sure what it would be though. Any chance you can pull them off the sanded and onto some of the rock a little higher to see if that stops the progression?

Both Acans (were) on rocks, the last photo shows it about 10cm off the sand. The other acan was sitting on the sand after its dip, it was glued to the rock above where the photo shows prior.

The first coral to show signs was the 2nd last picture (orange acan).

 

[Mr. Mojo Rising]

The nitrate and phosphate is very low, too close to zero for my comfort.

I would also ask what kind of lighting you have and what intensity. Looks like they are slowly withering away, it makes me guess either low nutrients or low light.

As you mention hammers and goni are on top of your rocks and are happy, this makes me wonder what is the par on the sand bed?

Just possibilities to review and cross off the list.

 

[Gumbies R Us]

If the coral up top are fine and the others aren’t, I suspect it’s a lighting issue. You could try and slowly raise your light over the next couple of days and see if that changes anything

 

[Sequest]

I spot checked the spots where the corals are not so great, PAR readings from my parwise are:
130, 152 and 101.

I think that is sufficient for LPS. I can raise light and with a quick test, my AI blade at 80% gets me par readings of 156, 195 and 137.
However that blows out the PAR at the top of the tank so 250~, which i dont think the hammers/goni's will appreciate.

There is an AI blade 24" and Kessil A360X on the tank. The Kessil is running 100%.

 

[Sequest]

One more thing to add
There has been an increase in nuisance algae in the tank. Nitrates used to be pretty low (1-2 tops), but 6.2 is the highest they have been. I cant find a reason for this, no dead snails (I normally pluck them when i find them).
I wonder if the nitrate is my concern.
I am also considering a mild dose of chemiclean just to see if it clears up some of this algae on the sand bed. Its not red cyano, its green.
Which in itself is weird because green hair algae is brown under blue lights, but this algae on the sand bed is green under blue light.

 

[Lavey29]

Corals especially LPS need nutrients and you essentially have none to offer them so they slowly starve to death. They decline from the inside and can take weeks or months to show the affects outward. Most LPS also prefer moderate lighting 125 to 250 par.

 

[Sequest]

Ill grab some phosphate up on the weekend, see if i can phosphate up from its low area.
That being said - the tank has been running very low nitrate and phosphate since day 1 without any obvious issues. But it is worth a try.