EDTA only delivers 1/10th(loses 90% effect) at PH 7.2 - The Planted Tank Forum
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post #1 of 11 (permalink) Old 04-13-2016, 09:48 PM Thread Starter
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EDTA only delivers 1/10th(loses 90% effect) at PH 7.2

I asked one of the many companies why they use the EDTA IRON instead of the DTPA iron and they were honest with me and told me it may have to do with price more than anything else.

I said that it would not work at all at my current PH levels and they send me an article showing that it might work a little with only delivering 10% and losing 90% of its effective IRON.

Seem that a low dosage of DTPA iron would deliver 100% of the iron to the plants and would be better if even dosed with an eye dropper vs a lot of this EDTA which will lose 90% of its effectiveness right from the start.

Is that your understanding as well or do I have it wrong?


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post #2 of 11 (permalink) Old 04-13-2016, 10:03 PM
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Hi SpaceLord,

Yes, that is my understanding as well. This is from a post I did last April on the subject (but I didn't have the great graphs you do - lol).
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If you are sure your PH will stay below 6.5 you can use EDTA. I would recommend the DTPA iron if there is a possibility your tank may be neutral to slightly alkaline. The percentage doesn't matter as much as the type of chelate.

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post #3 of 11 (permalink) Old 04-13-2016, 10:52 PM
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Hi All,

For the last 5 years or so I have been using "Grow More Organic Based 10% Iron Chelate" that I pick up locally at a hydroponic shop and have been having good results; it costs me about $14 for 8 ounces. Unfortunately the iron chelate in the Organic Based Grow More product is type HEDTA which provides me 25% -50% useable iron in a PH range of approximately 4.0 to 7.2. I try to maintain my tanks at a PH of about 6.8 but sometimes they vary. I'm going to look into the "Grow More EDDHA Iron Chelate 6%". A pound of the EDDHA costs about $24 shipped on Amazon and may prove to be a better value.

Here is another graph showing the available Fe based upon the type of chelate used and the PH of the tank
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post #4 of 11 (permalink) Old 04-14-2016, 01:40 AM
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I have to question how much is actually unavailable vs how much is readilly available. I can wholly see that floating plants would have issues obtaining iron dissolved in the water column, but rooted substrate plants manipulate the conditions around their root zone to make nutrients accessible. My memory is fuzzy on the specifics, but through diffusion in the water column the inaccessible nutrients should become available in the less oxygenated possibly lower pH substrate.

This would however explain why it seems everyone wants to dose higher levels of iron, far beyond what u would consider trace amounts


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post #5 of 11 (permalink) Old 04-14-2016, 04:12 PM
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As a chemist who uses EDTA frequently, this is very interesting to me. At high pH the issue is formation of iron hydroxides and iron oxides (rust) in place of the EDTA complex (or any complex for that matter). EDTA is most effective as a chelator at high pH, but most metals will precipitate as metal hydroxides at high pH so when using EDTA you must balance the two when you choose the pH. The graphs show the equilibrium concentrations - when we add micros to an aquarium it takes some time for the Fe to be released from the complex and reach that condition, so I wouldn't think of it as only 10% effective, rather it will be reduced both due to plant uptake and precipitation/loss of chelation over time.

The other aspect is that EDTA can be metabolized - EDTA solutions can grow mold if stored too long. That would cause the release of chelated ions over time too.

As theatermusic says, plants can manipulate conditions to uptake iron more efficiently. Iron is frequently limiting in many environments so organisms have become quite efficient at finding it.

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post #6 of 11 (permalink) Old 04-14-2016, 04:33 PM
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Quote:
Originally Posted by KevinC View Post

As theatermusic says, plants can manipulate conditions to uptake iron more efficiently. Iron is frequently limiting in many environments so organisms have become quite efficient at finding it.
Would you know whether a a piece of ferrous iron touching the roots of a plant would be a source? I've read that plant roots have the ability to chemically change the immediate environment and make nutrients available. I am not a chemist and get confused over it sometimes, but it appears so. If this is true, then it would mean burying iron beside roots is a viable iron source for them. So those who use soils, which will have some iron available, won't have a problem with dosing EDTA because it is available to the roots already. But those of us relying on liquid ferts either need to stick with DPTA or strap some ferrous iron to our roots....LOLOLOLOL!
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post #7 of 11 (permalink) Old 04-14-2016, 05:11 PM
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AWolf: I'm a chemist, not biologist, but yes plants can obtain their iron from nearby soils via roots. Some can excrete carriers for ferric iron (Fe+3) called siderophores, some can reduce ferric to ferrous (Fe+2), some rely on bacterial colonies to do this, etc. Metallic iron (non-oxidized) would be oxidized quickly to ferric (rust).

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post #8 of 11 (permalink) Old 04-14-2016, 05:33 PM
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Quote:
Originally Posted by KevinC View Post
AWolf: I'm a chemist, not biologist, but yes plants can obtain their iron from nearby soils via roots. Some can excrete carriers for ferric iron (Fe+3) called siderophores, some can reduce ferric to ferrous (Fe+2), some rely on bacterial colonies to do this, etc. Metallic iron (non-oxidized) would be oxidized quickly to ferric (rust).
Thank you. I've been wondering about this. LOL still.

Last edited by AWolf; 04-14-2016 at 05:44 PM. Reason: edit
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post #9 of 11 (permalink) Old 04-15-2016, 09:42 PM
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Would you know whether a a piece of ferrous iron touching the roots of a plant would be a source? I've read that plant roots have the ability to chemically change the immediate environment and make nutrients available. I am not a chemist and get confused over it sometimes, but it appears so. If this is true, then it would mean burying iron beside roots is a viable iron source for them. So those who use soils, which will have some iron available, won't have a problem with dosing EDTA because it is available to the roots already. But those of us relying on liquid ferts either need to stick with DPTA or strap some ferrous iron to our roots....LOLOLOLOL!
I'm not a chemist or anything like that, but I would assume you would run into problems if you just buried a bunch of iron in your substrate. While I've read of people putting nails in under sword plants and digging then up later and finding roots wrapped around them, I would expect you could very easily end up with toxic amounts of iron leaving into your water column which if memory serves interfaces with calcium and manganese uptake. Also you would have purity issues as most of the metal you can get today is actually an alloy with copper, buckle, titanium, carbon and numerous others in varying quantities.

Also some observations from nature. The lake where I spend my summers vacation has large plant colonies. There are also numerous spots with lots of metal (usually piles of nails from just to dose iron as we do currently fires or decomposing structures) and there is really no noticeable difference in growth of the plants from those areas with such metal and without.

Basically no reason you can't try it, but it's probably easiest just to dose iron as we do currently
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post #10 of 11 (permalink) Old 04-15-2016, 10:26 PM
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If you want to know more about Fe uptake through roots, google "strategy 1 & 2 iron uptake"

As for foliar Fe uptake. Some plants let the chelate (partially) enter the leaf, strip the metal (Fe2 or Fe3) and dispose the chelate back into the water column. Others take up the entire chelate, strip the metal and process the chelate inside.
Which plant uses what method and what the efficiency is, is unclear to me.
I've got a bunch of different iron chelates, and in general Fe-EDTA was enough to have good growth. But the addition or using only other chelates, always did something extra to the plants. Like with everything, some plants react better than others. The last couple of years i've completely banned Fe-EDTA, resulting in more efficient iron use.
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post #11 of 11 (permalink) Old 04-15-2016, 11:06 PM
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Interesting. My best planted tanks are all below 7 (5-6pH).
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