Yeah.... if you let it sit grungy like that it can happen. I'd still put it in the SG for a couple weeks, then let ISO sit in it for a couple more. Don't sweat the SG. It isn't going to adhere to the glass like gunk will. You just want to make sure you rinse it all out, and as you know it is pretty bubbly. So, once you see no bubbles shaking water in it, it is all gone. I don't soak my pieces in a bucket, but if really dirty let them soak with SG for a couple days/week, then ISO for a day or so, then rinse. Only use PBW rarely to bring them up to "brand new" clean. Do you know if you have hard water? I do and it will add white deposits like crazy. So much so that I buy distilled water for use and always give a rinse with this before setting out to dry. I have a couple different gallon jugs of it. For my first rinse after some tap water rinse I add a drop of alcohol to it and pour that back into one jug. This is my rinse jug. When pulling one off the shelf for use, I may give it a rinse with this or not, but always put much more fresh distilled water in than needed and shake it up before pouring out the excess.