It doesn't seem to progressing any further. The spots it is growing is getting quite thick, though. I think I am going to do some manual removal tonight, followed by a small water change to try and siphon out excess GHA floating around. Repeat in a few days, and see where I am at.
Sadly, my Yellow Tang is still nowhere to be found. The YT is always the first up and swimming around early in the morning and nothing so far. I can't see him anywhere in his usual caves and hang outs. If something did happen I don't think it would take long for the CUC to make him vanish. I'm starting to fear the worse. Just doesn't make sense, he appeared to be such a healthy fish, amazing color, and very active. Fingers crossed I'm just being paranoid.