Brain is sick

[C5flyboy]

I noticed this spot on my brain a few months ago but it never changed in size or anything until about three weeks ago. It has been growing slowly and I was wandering if anyone knew what it may be and what I could do for it? The only thing off on my water are my nitrates. They are at around 15. Everything else zero and Ph is 8.2-8.3. I do need to check my Calcium levels but wouldn't think low calcium would be the problem being everything else is doing great. Thanks for any insight anybody can provide

 

[Proseph]

What is your Mag at?

 

[C5flyboy]

Not sure cause I don't have a test for it but I would guess that it is ok as good as every other peice of coral is doing great and growing and two are in the process of splitting.