Thanks for all the feedback, I wasn’t sure either what side of the glass it was on. Either side scrubbing didn’t produce results to remove it. I’ll have to try PBW just isn’t readily available and I got my sweet cider lined up.
Trying to start up 5gal hard cider project. Last time I fermented was 5yrs ago. Gave my carboy a good cleaning and sat in Star sans overnight but I still have small remnants tucked into the grooves at the bottom. Do you think it’s safe?