Iron Gluconate vs Iron Citrate, and other iron questions

Aqua Lab Aquaria

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We have been experimenting with more iron dosing in our reef tanks and we have been trying to narrow it down to an optimal iron source. This was largely inspired by the DSR method.

From what I've read, iron gluconate (Randy's recipe) will give ferrous iron whereas iron citrate (DSR recipe) will result in ferric iron. In seawater, does one have an advantage over another? Or are they ultimately the same in seawater?

Furthermore, I have heard that iron gluconate will result in gluconic acid. Is this considered a carbon source for bacteria? I recently watched the Long Island Aquarium video by Melev, and in it Joe Yaiullo mentions using a special iron preparation with a carbon source and says they were having promising results. I wonder if this is iron gluconate?

Finally, I have been experimenting with iron gluconate along with iron EDTA 13%. For the purpose of phosphate reduction, I would assume that these are both good iron sources. My understanding is that they are weak chelators in seawater and should therefore result in a spike of iron that is then depleted through precipitation or otherwise.

I am also hoping to fortify the tank with iron for the purpose of supporting macoalgae growth along with zoox photosynthesis. Would IronDPTA be better for this? I am considering a mixture of all three and placing on a doser for continuous additions. The goal is to enhance macro health while using the gluconic acid and iron to help reduce nutrients/phosphates.

Any insights would be great!

Kent
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Randy Holmes-Farley

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FWIW, my current preferred DIY is ferrous gluconate using Fergon Tablet's from the drug store. It is cheap and easy, and I've been using it for many years now. :)

The citrate is also likely fine, but not as easy to DIY.

Citrate and gluconate are both going to be carbon sources, but the amount you are dosing is very, very small.

Iron EDTA is more complicated than the above two, IMO. IT is too strongly bound to be bioavailable, and needs to be broken apart by UV light before it is used. Tha tmay nbe fine, but might be quite variable tank to tank with different lights. Citrate may do that too, but is not as strongly bound in the first place.

I generally do not recommend adding enough iron to be very useful with respect to phosphate precipitation, and I'm not sure it does much when bound to organics.
 
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Aqua Lab Aquaria

Aqua Lab Aquaria

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I am using an iron gluconate powder from aquariumfertilizer.com. It has a very strong sweet smell so I assumed the amount of glucose was high...

My understanding is that EDTA is a poor chelator at the alkalinity of seawater. When I dosed .1ppm worth, that is what I tested using my Sera test kit; wouldn't that suggest it all quickly dissociated?

Kent
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Randy Holmes-Farley

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I am using an iron gluconate powder from aquariumfertilizer.com. It has a very strong sweet smell so I assumed the amount of glucose was high...

My understanding is that EDTA is a poor chelator at the alkalinity of seawater. When I dosed .1ppm worth, that is what I tested using my Sera test kit; wouldn't that suggest it all quickly dissociated?

Kent
Aqua Lab

Why do you think it poor? I thought it was expected to be quite strong in seawater. Spotte in "Captive Seawater Fishes" makes that claim.

I do not know how the Sera works or whether it detects EDTA chelated iron or not.
 
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Aqua Lab Aquaria

Aqua Lab Aquaria

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It was based off some aquaponics articles and also Tomm Barr. He states the following:

Practical pH stability range

Low end pH level High end pH level

Fe-EDTA 1.5, 6.5

Fe-DTPA 1.5, 7.5

Fe-EDDHA 3.5, 10
 

Randy Holmes-Farley

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biom

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A little bit out of the discussion here but Randy in your article about Iron you said "iron(II) citrate has turned brown and cloudy since I first made up the bottle years ago, suggesting that it is oxidizing to iron(III) and some is precipitating from solution, but I still use it. " How fast was this process of browning? I've made a bottle few days ago and it is still bright yellow with light green tint and no precipitation.
 

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