White Spot Spreading

[*Ruffian*]

I have had this coral for a couple of years and over the last month, a white spot started in the middle. It has started spread outward since then.

Water parameters have been stable. Only thing I have noticed is the crabs cruising across the top.

It has had good growth as it started as a square. Always been in the same spot in the tank. I don't think is is bleaching because it has always been at the same level and the light intensity has been the same for a year.

It seems like I am going to lose this coral.
Any thoughts?

 

[Hincapiej4]

Are you able to get some pics under whites? Also, seems a bit small for a year..

Are you running carbon by chance? Salinity/temp stable?

What are the things you've checked so far?

 

[*Ruffian*]

Are you able to get some pics under whites? Also, seems a bit small for a year..

Are you running carbon by chance? Salinity/temp stable?

What are the things you've checked so far?

Salinty1.026
Temp 78.
Ph 8.4
All 9.5
Ca 440

I have t figured out how to get a good picture with the lights. It has a greenish tinge. The coral started out at less than a 2" square. I thought that was good growth.

I did do a big water change where the temp probably dropped but I didn't check it. Could a temp swing cause something like this?

 

[Hincapiej4]

Temp swing definitely can, depending on how big.

 

[Hincapiej4]

Though most of the time, bleaching means too much light or the coral is starving.

Stn or rtn would be the water parameters, usually, imo.
I'm sure I'll be corrected if wrong.