Recurring mark inside demijohn glass

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Vinoors

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Hi All-

Has anyone ever noticed a mark within a glass fermenter that comes back regardless of cleaning or sanitizing? I attached a picture of a cloudy white circle inside my demijohn. This thing comes back year after year regardless of whatever cleanser, sanitizer, or carboy brush I use. I haven't noticed any adverse affects- the wine in this demijohn doesn't taste any different than any other demijohn that I have, but I'm perplexed as to what this is. It only shows up when the inside is dry, its not visible when wet. Picture attached.

IMG_0922.jpg
 
I bet it is actually etched into the glass slightly....you don't see it when it's wet right?
 
It looks like a hard water stain. At some point, water was left to dry with the demijohn on its side. If a hard water stain type cleaner doesn't remove it, it may very well be etched.
 
Yep, I second hard water stain. You often see the same thing on the old glass coffee pots where hard water was used.
 
Thanks for the feedback- based on the responses, it doesn't sound like something that would impact sanitation or affect must/wine.
 
It shouldn't be a big deal but depending on how hard the water is and what's in it, I know some opt to use spring water.
 

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