Pimples on tig?

[Dumptruck]

So I came home from a 5 day trip to find that my tig has grown what looks like white head acne pimples on his head, neck and some aligned neatly along the lateral line. I've been doing 50% water changes for the past 3 days it doesn't look like its getting any better. Has anyone had this before? Is it a precursor to SDS? Any help/comment will be greatly appreciated, Thanks!