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  • Black water produced; what's the cause of that?

    Our SDHW system is giving blackish water from the hot tap. It settles out as a black sediment, somewhat flocculent. At its worst, the black crud smears on one's skin as if used motor oil had been applied.

    The system is a drainback, about 6 years old, and our well water is very hard, so there is a water softener. I recently replaced the sac rods (magnesium), because it had been 1 1/2 years. The old sac rods were completely eroded, and the metal had been replaced by a grayish, semi-soft substance. Anyway, the new sac rods did not improve the 'black water' problem.

    Can anyone recommend a cure?

  • #2
    1. Get an analysis done of the residue. It could be chemical or could be the result of bacteria living off iron or sulfur in the water and the high temperatures. If the latter, you need to kill off the bacteria.
    2. Is the thermal system before or after the softener?
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      Do you have any heat exchanger, or does your domestic water get directly heated by the sun ?

      What is the plumbing - copper, galvanized, plastic ? Were dielectric unions used at each dissimilar junction ?

      Any electrical grounding jumpers "bypassing " the dielectric unions ?

      What is your backup hot water heat? What's the water PH ?

      I'm thinking with that much usage of the sacrificial anodes, you may have electric power flowing through your hot water, from something.
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      • #4
        Check out this web page for a lot of advice on a wide variety of odd water conditions.
        The internet consensus is that the most likely source is deteriorating rubber. If you do not use any rubber lined flex hoses, look for valves that contain rubber washers.

        Also, look at case number 6 at this site, and and also follow the link in it to "slime forming bacteria". If you have a high manganese concentration in your well water that might be part of the problem.

        If bacteria are part of the problem, then it may be affecting the well water but the bacteria are multiplying unchecked in the hot water system and tank.
        Last edited by inetdog; 11-04-2014, 12:17 AM. Reason: PS: twice
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #5
          Originally posted by Mike90250 View Post
          Do you have any heat exchanger, or does your domestic water get directly heated by the sun ?
          have heat exchanger...

          What is the plumbing - copper, galvanized, plastic ? Were dielectric unions used at each dissimilar junction ?
          all copper...;installer was aware of dielectric issues, and conscientious, so assume that's not the problem.

          Any electrical grounding jumpers "bypassing " the dielectric unions ?
          n/a

          What is your backup hot water heat? What's the water PH ?
          electric backup - pH unknown

          I'm thinking with that much usage of the sacrificial anodes, you may have electric power flowing through your hot water, from something.
          oh boy...

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          • #6
            Originally posted by inetdog View Post
            1. Get an analysis done of the residue. It could be chemical or could be the result of bacteria living off iron or sulfur in the water and the high temperatures. If the latter, you need to kill off the bacteria.
            will get analysis...
            2. Is the thermal system before or after the softener?
            softener before heating...

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            • #7
              Have you checked to make sure the softener is working properly by testing the water after the softener? Do you smell rotten eggs when running water?
              To me it sounds like hydrogen sulphide in your water, you most likely have sulphur bacteria in your DHW. The high water temps & magnesium from the anode rods help it to grow.
              Pull your tops to the toilet tanks to see if there is the same black residue present.

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              • #8
                Originally posted by LucMan View Post
                Have you checked to make sure the softener is working properly by testing the water after the softener? Do you smell rotten eggs when running water?
                To me it sounds like hydrogen sulphide in your water, you most likely have sulphur bacteria in your DHW. The high water temps & magnesium from the anode rods help it to grow.
                Pull your tops to the toilet tanks to see if there is the same black residue present.
                have not checked the water softener for correct operation, but had it serrviced recently by a trusted contractor.
                there is no 'rotten egg' smell; altho lots of evidence of iron in the water.

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                • #9
                  You can kill any bacteria living in your storage tank by heating to 160 degrees or adding bleach. Then flush out the tank

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                  • #10
                    Originally posted by epiphanatic View Post
                    have not checked the water softener for correct operation, but had it serrviced recently by a trusted contractor.
                    there is no 'rotten egg' smell; altho lots of evidence of iron in the water.
                    If using bleach - sodium hypochlorite - let it sit for at least 30 minutes before diluting/flushing.
                    [SIGPIC][/SIGPIC]

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                    • #11
                      Originally posted by russ View Post
                      If using bleach - sodium hypochlorite - let it sit for at least 30 minutes before diluting/flushing.
                      storage tank is 120g. how many gallons of store-bought bleach needed for tank that size?
                      (and thanks for info...)

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                      • #12
                        You can do a search for killing iron & sulphur bacteria in a well, should be the same procedure. Leave the solution in for at least 8 hrs since you can't agitate the tank to mix completely.

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                        • #13
                          In my water system I maintain 1 to 3 ppm in the sump which is 35 m3 - get some chlorine test strips - LucMan and the 8 hours is better since as he points out you have no agitation.
                          [SIGPIC][/SIGPIC]

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                          • #14
                            Originally posted by russ View Post
                            In my water system I maintain 1 to 3 ppm in the sump which is 35 m3 - get some chlorine test strips - LucMan and the 8 hours is better since as he points out you have no agitation.
                            He does not, however, want to use the stable continuous treatment level of chlorine. He wants to shock treat his tank, on the assumption that he will then drain and refill it to get to a near zero chlorine level, and possibly also shock treat his well (the volume of standing water) using the assumption that he will then pump out and discard several times that standing volume. (A 4" well casing holds about one gallon per foot of water depth.)
                            There will be good references with suggested concentrations (different for the two types of shock treatment.)
                            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                            • #15
                              Originally posted by inetdog View Post
                              He does not, however, want to use the stable continuous treatment level of chlorine. He wants to shock treat his tank, on the assumption that he will then drain and refill it to get to a near zero chlorine level, and possibly also shock treat his well (the volume of standing water) using the assumption that he will then pump out and discard several times that standing volume. (A 4" well casing holds about one gallon per foot of water depth.)
                              There will be good references with suggested concentrations (different for the two types of shock treatment.)
                              The shock concept I have trouble with - it is grossly overused in pool terminology. Seems like that is on the first page of the book all pool guys read. Just kill the bacteria with the normal low level of chlorine - it takes time. Even in an agitated system .

                              If one has a softener down stream the chlorine is not good for it - you need a carbon filter in between.
                              [SIGPIC][/SIGPIC]

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