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Calcium and Sulphate

Discussion in 'Advanced Strategies and Fertilization' started by srozell, Jun 2, 2005.

  1. srozell

    srozell Guru Class Expert

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    I was in the habit of dosing calcium carbonate in my CO2 tanks along with K2SO4 at my weekly water change.

    I heard rumor last night by a well respected aquariust in our area that sulphate and Calcium just bind together if they are dosed at the same time making them both unusable. Is there any truth to this? Should I change my dosing regime?
     
  2. Greg Watson

    Greg Watson Administrator
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    Re: Calcium and Sulphate

    Gee ... no one jumped in on this one ...

    A lot of times there is "truth" to a statement that something can happen or that something does happen ...

    The factor that needs to be determined is to what extent will it happen in a specific environment (most importantly yours) ...

    There are a lot of combinations that will occur ... even more that can occur ... but that does not necessarily mean that to the extent that it will happen or can happen, that it will have a material or statistically significant impact on your aquarium ...

    For a chemist, the process or sequence of combinations is easily understood ... most compounds will naturally seek a more stable combination ... there is a natural math to the process ... to the lay person like myself, it is easy for us to think about this in the context of oxidation (i.e. rust) ... certain compounds naturally want to combine ... however, will they combine all at once? Not necessarily ... so for example, different metals will oxidize (i.e rust) at different rates ... in most cases, this is a slow and gradual process ...

    Thus ... if a respected aquarist told you that calcium and sulfate will combine; I am quite sure that they are probably accurate ...

    What I don't know ... and is the most important question ... is how fast will this combination (reaction) occur in the context of your specific environment ...

    Did you know that some compounds will rust overnight yet other compounds will take years to rust? Some compounds will "oxidize" almost instantaneously with almost explosive results ...

    A very similar argument is made in aquatic circles about not dosing Iron on the same day that you dose phosphate ...

    In another thread ... Bill suggests that someone test to see what happens ... so I would encourage you to check it out for yourself ... setup two tanks and see if you can determine a difference ...

    As slow or as insoluable as most of us think that Calcium Carbonate is ... I am not sure that even a relatively good amatuer controlled test is going to be able to show a difference between dosing both together on the same day or dosing on alternate days ...

    Please understand that I don't personally know the propensity for calcium to combine into a sulfate form ... so all of the above is based on the assumption/speculation that indeed it will (since I don't have any reason to believe it won't) ... its still a helpful mental exercise to think through ...

    Greg
     
  3. Vladimir Zhurov

    Vladimir Zhurov Lifetime Members
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    Re: Calcium and Sulphate

    Solubility of CaSO4 in water is about 1 g/L or 1000 mg/L, meaning that in order for it to precipitate the concentration of Ca++ and SO4-- should reach 295 and 705 ppm, or higher. And this is HIGH in the context of freshwater aquarium. Such concentration of Ca will correspond to GH of approx. 42 degrees.

    So unless you are trying to mix CaCO3 and K2SO4 in one vessel at high concentration why should you worry?

    Regards.

    Vladimir.

    P.s.: edited to re-calculate proper concentrations of calcium and sulfate.
     
  4. Tom Barr

    Tom Barr Founder
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    Re: Calcium and Sulphate

    It would take a super saturated solution as Vadf points out, eg higher than seawater.

    You can use Ca(SO4), aka gypsum to dose also.
    You need to know the concentration, the solubility of each compound that folk's suggest will preciptate as well as pH/temp etc in many cases.
    Redox also plays a large role in the substrate and redox and pH are related.

    Regards,
    Tom Barr
     
  5. srozell

    srozell Guru Class Expert

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    Re: Calcium and Sulphate

    Thanks for the feedback.

    I won't worry about it. Things seem fine here so I'll leave it at that.
     
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