What happening to mushroom coral?

[EthanD152]

I just picked this guy up the other day. He’s been doing great so far. Normally fully stretched out and looking bigger than in the photo. At night he goes up like a ball. But I just did a water change and now it has two glowing spots and one of them started moving around above the skin of the coral? Not even sure how to describe it. Is it dying or is this fine?

 

[EthanD152]

Edit: forgot to add he also shrunk up a bit before the glowing spots appeared