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Unread 01/26/2010, 10:35 AM   #1
GTR
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Fe gluconate

Is Fe gluconate a good option for dosing iron? I didn't see it mentioned in your article but found a few references in other threads. I've had someone suggest that at a KH over 6 that DTPA would be a better option. In Seachems own forum they stated they don't know of any reason why KH would be the issue but instead said the lower the pH the more iron will be available.

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Unread 01/26/2010, 10:41 AM   #2
Randy Holmes-Farley
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I think the ferrous gluconate works just fine, and is what I use. You can use the Seachem product, or a DIY using Fergon tablets from a drug store (what I use).


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Unread 01/26/2010, 10:51 AM   #3
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Thanks. I have enough coming to mix up 12.5 L that will be equivalent to their product. 36.3 grams per liter to make standard 10,000 ppm solution. I will be adding some of their polycycloglutaracetal so it won't grow stuff in the bottle.

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Unread 01/26/2010, 01:36 PM   #4
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polycycloglutaracetal

Whre did you find that?


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Unread 01/26/2010, 01:56 PM   #5
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Sorry, Seachem Excel. It's either that or some HCL but I have the Seachem stuff.

Wonder what it would do in SW?

SteveU


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Unread 01/26/2010, 02:02 PM   #6
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I'm confused.

What do you have?


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Unread 01/26/2010, 02:27 PM   #7
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I try to say Seachem as little as possible in here.

Seachem markets a product for supplying a carbon replacement for CO2 used in FW planted tanks. The product is called Excel and contains polycycloglutaracetal.

At higher dosages than they recommend and used as a spot treatment it also might work as an algaecide. Seachem for obvious reasons won't discuss that.

Adding the Excel or (HCL) to the ferrous gluconate solution is suggested to stop it from growing slime. It takes me about 4 weeks to go through 250ml of the Fe solution and without something added I end up with some pretty gross stuff growing in the bottle.

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Unread 01/26/2010, 02:35 PM   #8
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Adding the Excel or (HCL) to the ferrous gluconate solution is suggested to stop it from growing slime. It

Who suggested that? Seachem? Either will probably work.

FWIW, I've never had anything grow in it, but I know that Cliff did.


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Unread 01/26/2010, 04:20 PM   #9
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I wouldn't ask Seachem how to DIY one of their products. That info was from a FW board.

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Unread 01/26/2010, 05:29 PM   #10
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OK, I understand.


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Unread 02/10/2010, 02:10 PM   #11
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Glutaraldhyde is a general biocide (cross links proteins) used in a great many things, I use it for slide sample preservation, but at about 2ppm, it works well as a carbon source of aquatic plants. Many species of lower algae, not the greens in general, do not like it, so there's some good selectivity in freshwater.

http://www.glerl.noaa.gov/pubs/fullt...5/20050003.pdf

It can be used a long term anti bacterial fungal agent also, and is somewhat common in the hobby. Not sure about effects in marine systems, inverts likely are more sensitive in general than say fish which are a bit more tolerant.

HCL can be used for the water solution, eg pool acid sold is often HCL so cheap, stinky and widely available as well as dangerous if the people do not do safe handling procedures.

Excel is a bit more forgiving.

Any strong acid can be used, removes the bicarb in the tap water used to make the solution.

I'd suggest using DTPA or EDDHA, not gluconates for Marine iron dosing.
With the higher alk/pH, they are far more bioavailable, stay in solution longer thus having far more contact time than gluconates and ETDA which are better for lower alks and pH's.

Gluconates are fine for daily dosing in some cases, or in conjunction with, a longer term chelator like the above suggestion.

Most of the aquarium brand names use the cheapest chelated they can find for marine products: ETDA, which is not the best choice from a horticulture/aquaculture standpoint. I use the chelators that are applied and appropriate for marine conditions.

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Unread 02/10/2010, 02:50 PM   #12
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I'd suggest using DTPA or EDDHA, not gluconates for Marine iron dosing.
With the higher alk/pH, they are far more bioavailable


How do you know that?

What mechanism of bioavailability are you anticipating?


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Unread 02/11/2010, 01:53 PM   #13
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Quote:
Originally Posted by Randy Holmes-Farley View Post
I'd suggest using DTPA or EDDHA, not gluconates for Marine iron dosing.
With the higher alk/pH, they are far more bioavailable


How do you know that?

What mechanism of bioavailability are you anticipating?
Plants take up Fe as Fe2+. Some might take it in as Fe3+, but chelate it at the cell surface before taking it internally with their own citrate or other chelators for transport.

If you put an iron compound such as iron nitrate in your solution, it will form a precipitate with other chemicals in the solution such as phosphate or good old rust. At higher pH (which is mostly controlled by the alk): Fe3+[aq] + 3OH-[aq] Fe(OH)3 [solid]. The chelating agents most frequently used in agriculture and horticulture are EDTA DTPA and EDDHA. EDTA forms a good stable bond with iron, manganese, zinc, copper and even with the secondary elements calcium and magnesium. DTPA and EDDHA are used for iron only to give extra stability and increase the performance of the iron chelate.

Gluconates of Fe etc do not last very long, minutes, maybe 1 hour or so in marine water (try testing this sometime, you will not measure much residual, even if you used the AA method at a lab). They are well suited for low alkalinity freshwater(say 50-80ppm or less) however or perhaps where daily dosing and an acceptable loss of a % of the Fe is okay. You get weaker bounds with these two than say EEDHA (thus an implied increase in bioavailabilty for gluconate, easier for the plant/alga to take up that formulation of Fe), but the trade off is that the bond is so weak, it quickly drops out and then is precipitated/wasted. I suspect some might still make it to the plant/alga however, but not much.

DTPA should last maybe a few days.
There's a reference below in seawater with Fe DTPA:

http://www.chelates-oilfield.com/NR/...1339/TL241.pdf

Not bad.

EDDHA, has the color trade off(bloody red), so less can be added, but it will persist in the chelated form far longer(days, but only at a low ppm since adding more will = blood red tank water, a trade off using it, good for low ppb dosing however ).

Once Fe is lost from the ligand/chelator, it's rust basically. Oxidized and not available. Not bioavailable any longer unless something is able to reduce it(eg an active DBS might, it's in that same redox range for Fe reduction, but not sure how long that will last once the Fe diffuses into the water column, not long I'd suspect). So I suppose it's not entirely wasted, but unless you have rooted marine plants, not much is going to removed from the sediment.

Few folks have rooted marine plants other than perhaps the rare hobbyists here or there, or a few mangroves in a fuge.

I think it's better to measure the Fe in the plant dry tissue to gauge what is the more effective chelator/ligand and NOT the water column. A plant/alga might be easily able to meet all it's needs without any residual being measured or persistent in the water column. That's the best test combined with the known dosing to the water column. Often times, nutrients/resources are used up and recycled faster than they can be practically measured. Gone before they can be tested.

It would be nice to do such dosing and dry tissue analysis for marine plants and the algae based on known amounts dosed to the aquarium of a known volume, PAR etc for various species.
Even coral would be interesting.

Here's a good explanation for the chemical properties of the various chelators:

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

As far as pH and Fe gluconate, these acids listed here are similar to gluconate:
http://www.springerlink.com/content/w9u4503618006986/

In crop soils:
http://www.sciencedirect.com/science...6d03dda787e26b

A good basic agricultural overview:



The citrate is pretty weak, and the gluconate ain't much better.

Given the trade offs, say mostly DTPA, say 90-95% with 5-10% of the EDDHA would be a good mix for adding Fe to marine systems.

I've used only DTPA myself for marine plants, but have some EEDHA laying around as well. Given the responses with ETDA and pH, I think most of the marine brand name trace mixes all use ETDA, which is a poor choice for the applied pH of marine systems.

1 pound of DTPA would supply a 200 Gallon marine system with high plant/algae density for maybe a decade or so.

I think the issue of energy required to break the weaker bonds with the gluconate, citrates, ETDA to take up the Fe is mute however. Fe demand and the energy to break such bounds is very low to relative expense and allocation of energy for the plant/algae.

I think a strong bond + longer exposure seems like a better management plan.
But adding a mix of say ETDA(2 part)+DTPA(8 parts, and (1 part) EEDHA might be wiser still.


Regards,
Tom Barr



Last edited by Plantbrain; 02/11/2010 at 01:59 PM.
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Unread 02/11/2010, 04:11 PM   #14
Randy Holmes-Farley
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Well, you present the case for strong chelation, but not necessarily efficacy in a marine aquarium. I specifically selected ferrous gluconate (and before that, ferrous citrate) to be a weak chelator.

Without a doubt these weak chelators work very well in a marine aquarium. One can see Caulerpa green up rapidly by dosing these when iron has been limited and the macroalgae is yellow. Citrate has been used for decades for this purpose. I got the original citrate recipe years ago from one of Martin Moe's books (IIRC).

According to Spotte in Captive Seawater Fishes, EDTA is too strong of a chelator to allow bioavailability, and the iron is only available when UV or oxidation rips the EDTA apart. Same may apply to other strong chelators.

I do not assume the iron is staying bound to the gluconate. I expect there are many other natural chelators in the water, and these likely bind and hold a lot of the metals present in the water (copper, iron, etc).

In any case, it could be that the weak chelators are better or worse, but they all seem to work adequately and probably that is because we add so vastly more than is actually needed.


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Unread 02/12/2010, 01:38 PM   #15
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[QUOTE=Randy Holmes-Farley;16569141]Well, you present the case for strong chelation, but not necessarily efficacy in a marine aquarium. I specifically selected ferrous gluconate (and before that, ferrous citrate) to be a weak chelator.
[quote]

As do I.

Quote:
Without a doubt these weak chelators work very well in a marine aquarium. One can see Caulerpa green up rapidly by dosing these when iron has been limited and the macroalgae is yellow. Citrate has been used for decades for this purpose. I got the original citrate recipe years ago from one of Martin Moe's books (IIRC).
Yes, there is a long history in phycology of usage for these types of Fe.
While they do work, the question is how long they remain, thus their dosage(concentration X time).

The needs might be met since all that is needed is a weak pulse of Fe.
In a strongly limited case, one would expect to see dramatic results either way(no matter what type of chelator was used). So simply suggesting that it "works", does not show one will yield better growth than another. My speculation is more driven by the latter.

Which would yield a better exposure of Fe to the marine algae/plants?

Quote:
According to Spotte in Captive Seawater Fishes, EDTA is too strong of a chelator to allow bioavailability, and the iron is only available when UV or oxidation rips the EDTA apart. Same may apply to other strong chelators.
Errr..........for fish or for plants/algae??? For humans and fish, say in their food, I'd use citrates and gluconates, eg vitamin ingredient list.
Adding it to fish food for Fe supplements, sure.......

However, I'll strongly dispute and backup what I say about plants/algae taking up such forms of Fe: Plants and algae, marine or otherwise can and do use ETDA/DTPA and EDDHA, taking the entire complex and leaving the chelator outside externals, and takes the Fe internally where it has it's own endogenous chelator(citrate perhaps in grasses/higher plants, some algae).

This is very well demonstrated

Diatoms:
http://www.jstor.org/pss/2835965
Macrocytsis:
http://www.plantphysiol.org/cgi/reprint/68/4/914
http://rms1.agsearch.agropedia.affrc...ty/56-0800.pdf
You can see Fe uptake levels off for Laminaria in figure 3.
Seagrasses:
http://www.jstor.org/pss/2838710
http://www.int-res.com/articles/meps/16/m016p045.pdf

Most studies use these for nutrient growth medium going back to Hoagland's modified.

Quote:
I do not assume the iron is staying bound to the gluconate. I expect there are many other natural chelators in the water, and these likely bind and hold a lot of the metals present in the water (copper, iron, etc). In any case, it could be that the weak chelators are better or worse, but they all seem to work adequately and probably that is because we add so vastly more than is actually needed.
True. I'm suspcicious of natural chelators in the water. Floc perhaps.
If we would argue for efficacy of the chelator, then something like EDDHA and DTPA would be preferred however.
Do these make a difference?

Well, it is a trace, after all, so I would not predict dramatic differences except where they are strongly limiting, compared to say limiting N.

But it might make dosing less frequent and perhaps getting more Fe to the plants/algae. It's also cheaper. Lots.

I have to wonder, while using weak chelators does "work". does using stronger DTPA etc work better?

Weak chelators also work well in FW systems, however, using a mix of several, Gluconate+ ETDA+ DTPA covers all the bases. While there might never be the research to support one over the other experimentally, we can hedge the bets and use ones that add weak, medium and strong bond strengths along with short medium and longer scale time frames of exposure.

I think the issue of persistence of the chelator brings up an interesting issue in reefs and where few water changes are done. Gluconates are rapidly decomposed, where as the DTPA and ETDA are not nearly(see DTPA reference above).

However this might balance with the lower dosing required using DTPA etc to have the same effect. The best way to measure that might be with something like Ulva and measure the % of Fe in the dry weight biomass taken up via the 5 chelators, citrate or glycine say, Gluconate, ETDA, DTPA, and EDDHA over time. The test is not a complex test to do.

The total % of Fe taken vs the % dosed would give a relative difference for Ulva. I suppose several species could be done and measured for a large comparative model. then you could answer it, but based on agricultural perspective, you'd get better efficacy using a blend or the strong chelator.

In otherwords, if I grew commercial macro algae, I would not use gluconate.
I'd use DTPA.

So why do most Fe supplements sold on the market use ETDA?

Why waste all that Fe if we can do better?
Why not see and try something as mix of several chelators to cover all the bases? Then the algae/plants can chose regardless of out assumptions.

Well, that's the management side talking there


Regards,
Tom Barr


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Unread 02/18/2010, 11:26 AM   #16
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FWIW, Spotte was referring specifically to phytoplankton uptake of iron, and quotes a lot of papers on the mechanism of uptake using various chelators.

He concludes EDTA is OK, but only because it breaks down over time (a few days).


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