Disappearing magnesium

Discussion in 'Reef Chemistry by Randy Holmes-Farley' started by Trailermann, Aug 15, 2017.

  1. Trailermann

    Trailermann Well-Known Member

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    Here is my problem. I need to supplement my magnesium daily to keep the level above 1200, even though the concentration of kH and Ca remain relatively stable. Each day I am adding 25 ml of liquid magnesium supplement.

    The many experienced reefers in my local club are stumped.

    30 gallon JBJ nano tank.
    Well established rocks and sand (2 years).
    mixture of LPS, few SPS, snails, and 3 small fish
    Nano calcium reactor, 2/3 calcium carbonate and 1/3 magnesium granulate
    Hydor slim skim
    Modest feeding every other day.
     

  2. CodyRVA

    CodyRVA Well-Known Member R2R Supporter Build Thread Contributor

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    What exactly is your "liquid magnesium supplement," as in brand or product type?
     
  3. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    There are only three possibilities when alkalinity is not being consumed (which isn't the case here, see next post)

    1. test error (likely the explanation)
    2. water changes with a low magnesium mix
    3. A drop in salinity (drop from 35 to 33 ppt drops magnesium from 1280 ppm to 1207 ppm)

    Magnesium cannot drop any other way if alkalinity is not being consumed.
     
  4. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    Ah, I see you are using a CaCO3/CO2 reactor. So you are consuming alkalinity and calcium. Do you know how much alk per day you are supplying?
     
  5. Grey Guy

    Grey Guy Well-Known Member

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    I have the same problem. I can dump Mg. Supplements liberally and not ever reach 1300 ppm and by the next week can be at 1000 ppm. I don't have much bio load and the only thing consuming Mg. I think is coralline algae.
     
  6. Trailermann

    Trailermann Well-Known Member

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    I wish I knew. Before installing the reactor, I was adding 2 tsp of SeaChem reefBuilder a day. My pH is 8.0.
     
  7. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    Test error for sure (or a salinity change).

    To consume 200 ppm of magnesium into coralline algae would consume well over 1000 ppm of calcium and 150 dKH of alkalinity.
     
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  8. Grey Guy

    Grey Guy Well-Known Member

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    O.K Thanks. It's been the same since I started my tank. But then I had a calc reactor. I have gotten the same results from Nyos and Salifert. Question. I'm going with live rock, fish and softies. Do I need to be concerned with magnesium in my type system?
     
  9. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    Magnesium is worth maintaining at natural levels (about 1300 ppm).

    How are you supplementing calcium and alkalinity? If you use a good two part, you likely don't need to worry about magnesium since they will have enough for most situations.
     
  10. Grey Guy

    Grey Guy Well-Known Member

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    I was going to use Kalkwasser. Read that Mushrooms prefer a PH of 8.2 or so. I believe my salt mix has some Mg. In it.
     
  11. Trailermann

    Trailermann Well-Known Member

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    ESV B-ionic Magnesium from BRS
     
  12. Trailermann

    Trailermann Well-Known Member

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    Randy, let's see if I understand this right. Magnesium is consumed, on a proportionate basis, in the same fashion as calcium and alkalinity. Reef building corals as well as coraline algae consume all three. There is no other avenue for magnesium to deplete. All this assumes steady salinity.

    BTW, my Red Sea test results compare well with two different LFSs. Would increasing the percentage of the magnesium granulate in my calcium reactor reduce the need for daily manual supplemental dosing?
     
  13. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    Correct.

    There is no likelihood that you are depleting 25 mL worth of B-ionic Magnesium each day in a 30 gallon tank.

    That's 8 ppm of magnesium per day. Real magnesium demand will be very roughly 1/10th of the calcium demand.

    Have you measured the salt mix you are using for water changes?
     
  14. Greggy

    Greggy Member

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    It's more important to keep your magnesium 3.25 times your calcium. And keep the Alk at a good level. If you increase the magnesium increase the calcium to match
     
  15. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    Why?

    I understand that the natural ratio is about 3.05 (weight based), but if one wanted magnesium higher for some reason (such as to inhibit precipitation of calcium carbonate on pumps), there's no reason that I can think of that calcium should also be raised.
     
  16. Greggy

    Greggy Member

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    Yes. I run my magnesium at 1600. And my calcium approx 500
     
  17. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    What would be different at 1600 ppm magnesium and 420 ppm calcium?
     
  18. Greggy

    Greggy Member

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    High calcium or magnesium is fine. If you run an SPS tank then up the calcium a bit. If not drop the magnesium a bit. I feel the ratio plus Alk is more important that the exact amounts you are running.
     
  19. Randy Holmes-Farley

    Randy Holmes-Farley Reef Chemist Staff Member Team R2R R2R Supporter R2R Excellence Award Expert Contributor Article Contributor

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    But why do you think the ratio is important?
     
  20. Greggy

    Greggy Member

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    It was explained to me years ago. I know people with low magnesium and high magnesium have great tanks depending on what corals they have. If I remember correctly I think natural seawater is 1300 mag and just over 400 calcium which is perfect ratio. My magnesium is 1600 and my calcium is 500 approx. I am upping my magnesium a little at the moment
     
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