Carboy brush left rust stain in glass carboy

[tonymark]

I was brought away from cleaning a glass carboy last week and left the carboy brush in it for a couple of days. The metal in the brush rusted and left a rust spot in the bottom of the carboy. Tried bar keeper's friend, and didn't have much luck. It has pure bleach soaking in it now.

Any ideas how to remove the stain? Thought some undiluted star-san may do it. I have NaOH and HCl. Thinking the HCl will do it, but I really don't like to mess with that stuff.

 

[IslandLizard]

Barkeepers Friend should do it. Stick a damp rag in there with it and scour it out, using the carboy brush as a handle.

Next thing is soak the bottom in some Hydrochloric Acid (hardware store). It reacts with and converts rust to Ferric Cloride, that washes away.
Careful though, that acid is nasty. Goggles, old clothes, protective gear, gloves and all. No kidding!

I have black metal "streaks" in the necks of all my carboys. I guess it's Zinc deposits from the carboy brush's galvanized metal wire. Very hard to remove. Once in a while when I get the urge, I remove it with a drill and an attachment and some scouring powder. Hardly worth the hassle. It doesn't seem to harm anything. Your rust may fall in the same category. It's a very thin layer that clings, or discolored the glass.