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Wow i didn't realize gluconate was such a weak ligand

Discussion in 'Advanced Strategies and Fertilization' started by ordloh, Oct 7, 2009.

  1. ordloh

    ordloh Prolific Poster

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    Had some free time today so I looked up the formation constant of iron(II) gluconate, apparently the K value is 10 :confused:
    The formation constant of iron(III) gluconate is 10^37 :confused: :confused:
    can tom or someone verify this? I got these values from SpringerLink - Journal Article
    I don't think these values are correct, it means most of the iron (II) will be precipitated out of the water and iron(III) will be almost impossible to remove from iron(III) gluconate.
     
  2. Tom Barr

    Tom Barr Founder
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    I'm not sure, Chem is part of my background, but not in ligands, I know enough ow work through issues, but it's not particularly something I worry about.

    I worry about how much of Fe Gluconate I need to add to get the best growth, the way the plants appear aesthetically and is the product economically good for dosing given the first 2 issues.

    The theory and formation constants are nice to have as well, but the bottom line are really those 3 things above.

    Regards,
    Tom Barr
     
  3. ordloh

    ordloh Prolific Poster

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    thanks for the reply. I agree that the end result is the focus for aquarist. I usually like to do a bit of theory before trying out a new product though since it might save me some money. I've only recently swtiched from a generic locally made trace mix which uses EDTA to seachem flourish so I haven't been able to observe any changes in plant growth yet. Flourish seems like a promising product from anecdotal evidence on all the forums i frequent, even though the theory says otherwise XD
    right now i'm guessing that the when dosing iron, most of the iron in the aquarium will exist as iron(III) gluconate (due to the ridiculous bond strength) and the gluconate ligands are easy for the plants to metabolize, releasing the iron.
    also, i've been using seachem equilibrium to dose potassium (can't get KNO3 here) and i noticed it contains 0.11% soluble iron. Since i'm dosing phosphate in large excess to the iron as well, almost all the iron is going to be precipitated out. If i add gluconic acid to the water however i'm pretty sure the iron will be ripped out of the precipitate.
     
  4. Tom Barr

    Tom Barr Founder
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    Well for ETDA, a optima of 6ppm is good/best for Hydrilla's Fe demand.

    Can we do fine dosing it at .6ppm?
    Certainly.

    How much gain do we get?

    We can talk bond energy etc and uptake, but overall, plants adapt and make do pretty well, does it affect rates of growth?

    Not much, as long as you do not get "too limiting". That's semi arbitrary to most aquarists however. More so for traces than say NO3, PO4, K+ and certainly many more X's than CO2/light.

    I can certainly see a difference at higher trace additions/frequencies vs less, this occurs even more at higher light, but it also means you MUST have good light, good CO2, good macro nutrients, and good general care and good healthy plants to start with.

    I recently got a lot of dry Fe gluconate( 60lbs).

    I think SG water is pretty soft overall, lower KH. I have similar water here in CA from the mountain snow melt(Likely even better). So this form of Fe is pretty good at lower KH, at higher KH, or if you want the Fe to hang around for a few days, DTPA will work also, or a mixture of several chelators/ligands.

    Then the plants can take up what ever they so chose over a few different time scales.

    Regards,
    Tom Barr
     
  5. ordloh

    ordloh Prolific Poster

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    kk good to know. to be honest I haven't seen any noticable difference in plant growth with varying levels of traces or different chelators. I'll try increasing the dosage to see if there's any difference. The plants seem to do pretty well at very low dosages or just plain tapwater, maybe it's because i haven't tested the upper limits of all the parameters yet. Anyway my question about ligand strength and all that is just stuff i enjoy thinking about, pity it doesn't have any real application in an aquarium (my thoughts always drift to aquariums)
     
  6. Tom Barr

    Tom Barr Founder
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    Well , you never know where an idea might lead to, generally nowhere:0
    But every so often, it can lead to some cool things.

    The ligand and chelator bond energy have been discussed and the biological aspects of uptake, as well as inorganic chemical effects on old APD digest post from myself, Miller, and Morin from day's past.

    You can check there if interested in older discussions.
    Roger went after the inorganic side, I went after the biological side, Greg discusses the gluconate.


    Regards,
    Tom Barr
     
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