White patch on hammer

[shrimpy smell]

Found this white patch on my hammer coral this morning. Anyone have any idea of what it could be?
Water parameters:
Salinity 1.025
Alk 8.8
Mag 1300
Calcium 450
Nitrate 4.5
Phosphate 0.02
pH 8.2
I had a jump in alk at the beginning of April (~10.8) but have be slowly lowering it back to where it is now. Over the last week my hammers, frogspawns, and torches haven't been fully open, no exposed skeleton so far. Everything else in the tank including gonis, alveopora, zoas, mushrooms, and acans have been looking the same as usual

 

[goosemans]

Hard to tell from that angle. If it moves around it could be a euphyllia eating flatworm

 

[shrimpy smell]

Thanks for the quick reply. I'll keep an eye out for any movement

 

[Shirak]

Big white patch below it also, from very rapid tissue loss on the outside of the skeleton.

Don't know if the alk swing had anything to do with it. Not very likely but your nutrients are very very low to 0. PO4 at .02 could easily be 0 due to testing accuracy for hobby kits. NO3 at 5 low too. Not good for most LPS. Should be looking around .05-.1ppm for PO4 and 10-15ppm for NO3.

 

[kevgib67]

^ This and I would bump your magnesium up. Shoot for 1350 but mine really thrive at 1400 or a little higher.

 

[Shirak]

Pics of the other corals? What are you using for light? Looks a bit dim but that can be deceiving.

 

[shrimpy smell]

Everything is looking good now, I figure it was some sort of bacterial issue. I dipped everything in brightwell Medicoral, the hammer in the photo was dipped twice. It's been about 2 weeks since then and everything is fully open again. Running an ai hydra 32hd, the photo was taken earlier in the day so it wasn't the brightest. But the corals having the issue were under 150-240 par. I've increased my Mag to sit between the 1350-1400 range. Thanks for the help!