I left oxy clean in two of my carboys for 3 weeks and some kind of build up formed on the inside. With some research I found out I needed to use an acid. I used some vinegar water and that did nothing, then I used star san and that did nothing. Finally I had to use caustic acid and that did it. It took 6 hours or so to dissolve the build up.
I learned my lesson, max overnight when i comes to oxy. I do not know if PBW would do that if left long enough.