What is this junk?

[jostafew]

Good sleuthing. I did dose vinegar for about 8 months in an attempt to control nuiscance growth, but while it did seem to help the problem a little the biggest change was rendering my skimmer nearly useless by producing crazy resiliant bubbles that plugged it up and blew the lid off it. I slowly phased out the carbon source about a couple months ago. Since I've quit the carbon skimmer behavior has gone back to what I would consider normal.

Yeah it's lighter color when it's thinner. I will snap another pic when the main daylight lighting comes on.