I racked my Nut Brown ale last night and washed out the bucket and there is a stain ring. This was my third batch in this bucket. I tried using bleach to get it out and it sort of worked, but there is still a residue. Is this something I should worry about? What works to remove it? I left my starsan solution in it overnight too, but it was still there in the morning, but I wasn't expecting it to do anything.