Advice? Anyone seen this before?

Anyone ever seen this before on a cap? Started in one spot and has increased a bit. My alk dropped and nitrates are a bit high at 30 but thought I would post as I get these things back in check.

 

I've had an issue similar in the past as fish poop or food built up blocking it from light then it would turn white. Maybe not enough flow. Or a fish could be irritating the coral.

 

I've had it happen when my Mg in tank got below 1325.

 

Appears to me as toxic bleaching. Likely means ammonia, nitrite, phosphates or Nitrates out of line. Color is good originally so I wouldn't say lighting or flow. You recently tore tank down and moved things around twice. Could of had a very MINOR spike of ammonia. As long as things in check, should recover in 4-5 days.

 

Also check for monti eating nudis. They are incredibly tiny and come out at night. Just one or two of the 3-5mm ones can eat a colony whole in a week. I just managed to eliminate mine with a strict 'selection pressure' regimen.

 

It's been progressively getting worse last couple weeks. Original spot is healed but new spots have been gradually popping up. Tried looking for nudi underneath last night but not with the lights off. I'll look closer tonight to make sure that's not an issue.