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Thread: Blue stains in the bathtub... confused as to why.

  1. #1
    DIY Junior Member bluestains's Avatar
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    Default Blue stains in the bathtub... confused as to why.

    I have copper pipes. The stain in my tub is blue ... not green, not green-blue, not aqua, but blue. Everything I've read seems to suggest copper corrosion, but I tested PH before and after the softener and it's consistantly 7.5.

    Now the likely culprit is hydrogen peroxide. I have a peristaltic pump and inject H2O2 to fix my sulpher smell issue. The hydrogen peroxide is fantastic... no rotten eggs, and my excess iron drops out of suspension for easy filtration giving me water that smells great and doesn't taste like metal. However, it appears the peroxide is corroding my copper. My understanding is that that should not be happening... especially in non-acidic water. What gives? I'm injecting the peroxide at 25ppm with a mixing tank in the line. Is the copper/peroxide combination a no no or do I just need to reduce the h2o2 concentration?

    As far as I'm concerned, no h2o2 isn't an option. I can't go back to rotten egg water. I would rather convert all my plumbing to pex. Side note: I also use Morton rust remover pellets. Could the citric acid be mixing with the peroxide to form something corrosive?

  2. #2
    DIY Senior Member Smooky's Avatar
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    Default

    There are many things that can effect how corrosive the water is to copper pipes, not just the pH. There may be improper grounding of the electrical service causing electrolytic dissolution of copper or a small appliance improperly grounded to the plumbing. If it is the water quality there is something called the “Langelier Saturation Index” that might help you to figure out what is causing your copper pipes to corrode. It is a formula that determines weather your water is neutral, scale forming or corrosive. You need to know temperature, pH, Total Dissolved Solids (TDS), Alkalinity, calcium carbonate etc. Carbon Dioxide causes corrosion in copper. Water softer than 50 mg/l CaCO3 is corrosive. There can be many other reasons. I always like to start with a complete water analysis.

  3. #3
    DIY Junior Member bluestains's Avatar
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    Default think I figured it out

    While I didn't see it mentioned anywhere before, apparently the H2O2 and copper pipes don't get along. I don't know if this is true of all water, or just mine, but I did a little test. I dropped a couple old pieces of copper pipe that I had cut off during a bathroom remodel into a glass of water. I then added a couple drops of the h2o2 I use which is 35% food grade. While this concentration ended up being considerably higher than what is actually in my pipes at any given point in time, it proved to me beyond a reasonable doubt that the hydrogen peroxide was causing corrosion on the copper pipes. The old pieces of copper bubbled all the old black deposits off and then rapidly started corroding into a nasty blue green finish. I'm going to try cutting the level back as far as I can, but I need enough to take care of the sulfur smell... it's really awful. I dropped it by 2/3, but I have my doubts that so little will take care of the smell. Time will tell.

    The only thing that is still odd to me is the color. The stain in my tub is far more blue than the blue/green corrosion I'm seeing. Maybe it's just the bathroom lighting.

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