Can Mg dosing drop pH and KH?

Discussion in 'Water Parameters and Additives' started by Bendor, 30 Jun 2013.

  1. Bendor

    Bendor

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    250 liter tank
    Ca 430
    KH 6.1
    Mg 1200
    pH 8.0

    Dosed 250g of MgCl over 2 days. Mg increased to 1280ppm, KH dropped to 5.2 and pH to 7.7.
    This was checked at 11h30 AM but the tank lights were still off, curtains open, no direct light and corals mostly closed so I assume normal night time drop in alk and pH could play a role.

    I haven't read anything about Mg dropping either pH or alk and was wondering if anyone has experienced the same.
     
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  3. Bonehead

    Bonehead

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    As I understand it Mg in the solution ( ie not bound to other compounds) will preferentially form MgOH in solution. This takes OH out of your solution increasing the relative concentration of your H ( and therefore your pH wil decrease).
     
  4. Bonehead

    Bonehead

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    Your buffers are trying to cope with the decreased pH and therefore your TA has decreased ( ie your buffers have decreased) . To fix add buffer
     
  5. Nemos Janitor

    Nemos Janitor

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    Yup adding Mg to "fast" ( increasing the Mg to quickly) will decrease the O2 in the water. This will cause the ammonia to rise and CO2 to rise (Henry's law) and PH to drop due to the high CO2.

    You will need to increase gas exchange at the water surface to stabilize.
     
    Last edited: 30 Jun 2013
  6. Bendor

    Bendor Thread Starter

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    Thanks @Nemos Janitor

    How fast is too fast? I added 100g MgCl in 1000ml RO dripped in over a hour one night and 150g in 1.5 liters RO over 2 hours the next night.
     
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  7. Nemos Janitor

    Nemos Janitor

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    Each system depends on the demand on O2. Recommended is not to increase Mg by more than 30-50pp per day.
     
    Last edited: 30 Jun 2013
  8. Bendor

    Bendor Thread Starter

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    Thanks.
     
  9. Nemos Janitor

    Nemos Janitor

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    Great, keep us updated on the progress.:thumbup:
     
  10. Bendor

    Bendor Thread Starter

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    I added 10g of sodium carbonate in 1 liter RO over 2 hrs this afternoon.

    Alk up from 5.2 DkH to 6.7
    pH up from 7.7 to 7.9

    Plan to do it again on Tuesday morning when at the low side of the pH swing.

    What do you think?
     
  11. Nemos Janitor

    Nemos Janitor

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    What is your Mg level now?
     
  12. Bendor

    Bendor Thread Starter

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    Mg 1280 ppm
     
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