Tried pretty much everything. Iso, grunge off, pwb, alconox, and vinegar. Like I said this was my first rig so I wasn't super careful with it and didn't clean it frequently.
This all started after going on a few months without cleaning and daily usage. I decided to pour out the water and do an iso soak. It was dirty but not like super gross. There was this strange film that was on the bottom right under the stem and also some sort of hanging film on the bottom of the stem itself. I also noticed a few small flecks on the bottom that wouldn't come off either. These were still present after like a week long iso soak. Thats when I stumbled upon the pbw thread and subsequently discovered products like alocnox, grunge off, and simple green. Tried em all and got rid of the hanging film on the bottom of the downstem but the film on the base and small particles still remained. Plus I had these white stains on the side from the pwb/alconox. I've since bought new rigs and am now a little ocd about cleaning. Which brings me to the situation I'm in....really didn't need to get it clean I just really wanted to! My wife was giving me a hard time about this....she was like "ugh does it cause any problems function wise...if not I wouldn't worry about some small white film you can see when holding up to the light" But like I said ocd....it was driving me nuts.
Either way, from now on I have a large glass lock container that I have filled with simple green and just let all pieces soak in it overnight. Pull them out the next day and rinse...crystal clean. I am a little concerned about any sort of lingering chemicals in the simple green but I have yet to read anything that scares me enough to go back to iso. They say eco-friendly but i do worry about any long term residual buildup on glass we use to vape out off of.
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.