|Not my tub|
Today while reading my email there was an ad for Hometalk, a home improvement site where you can make boards like Pinterest. I've spent time on there in the past so I thought I'd go see whats new. Well I ended up on a board and saw a tip on how to remove rust stains from a tub. It prompted me to Google blue/green stains and then I found my cleaning answer! (Why I never thought to Google an answer in the past can only be explained by the fact that I'm middle-aged and Google wasn't around to answer my life questions for the majority of my life so I don't always think of it).
I immediately jumped up and had to try it (I was still in my pajamas). Vinegar! I poured white vinegar straight from the bottle on the blue stain and like magic it went away. It even got the stain from where the tub finish is etched around the drain (it's a 60 year old tub). Apparently the water is acidic from the dissolving copper pipes and you clean an acidic stain with an acid like white vinegar.
It does make me wonder what this lovely acidic water I have is doing to my skin and hair. Maybe this is why my hair looks like a haystack (well a graying, mousey brown haystack).
So now you know. Blue stain cleaner = white vinegar