Calling PigletJohn! Blue staining under bath tap

[theconstantinoplegardener]

Dear @PigletJohn,
Over the past few weeks, our metal (enamel?) bathtub has developed a blue-green stain running down from the tap (photo attached). It seems like some sort of deposit which can't be rubbed off; I don't think it's mould. We live in a hard-water area but we have softened water (using salt). The tap is a thermostatic tap which was recently repaired and the staining seemed to get worse at about that time. What could be causing this problem and how can I remove the stain and prevent it from returning, please? I thought it might be corrosion of the pipes caused by acidic water, or electrolysis, but it seems to have come on so suddenly and I can't imagine why either of those things would suddenly get worse when the thermostatic tap was repaired.

copper staining. after plumbing work, bare untarnished copper is exposed inside the pipes and tends to tarnish, leaving copper stains from dripping taps. A bathroom cleaning spray like "flash" might remove it, possibly with a green nylon pan scourer.

I think soft water makes it worse because the inside of the pipe is not coated with limescale. It will probably stop once the inside of the pipe tarnishes.

Thanks so much @PigletJohn, I'll try Flash and a nylon scourer. Much appreciated!

the bathroom sprays (unlike the floor cleaner) contain some kind of scale-removing chemical that seems to help.

You need something mildly acidic to get rid of a copper stain. Try salt dissolved in white vinegar, or the classic vinegar and sodium bicarbonate or lemon juice. I would do a test somewhere inconspicuous. If it doesn't come off straight away, you might need to soak a cloth in it and leave it on the stain.

Thank you both! I do actually have white vinegar and bicarb of soda already, so I will try them first and then buy some Flash if necessary.

Lovely to see PigletJohn about.

@PigletJohn is like the plumbing Batman of Mumsnet! Send up the Piglet signal and he will come to the rescue

Love the idea of the Piglet signal

My tenant complained of blue stains in the bath from a leaking tap. She tried to get it off and rubbed the enamel off and wants me to pay for a new bath

Blue stains from leaking tap I didn’t know about, she didn’t use a bucket or anything to stop staining. Her and her dad tried a number of solutions to try and clean it off but they’ve rubbed the enamel off and wants me to provide a new bath