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Discussion Starter · #1 ·
Yesterday, i mentioned that ETDA iron may not be as stable as HEETA or DTPA. Iron in ferts. Today, i noticed a 2nd post mention EDTA to Bind Heavy Metals. I wondered about the differences of Fe vs other metals, so I thought i would investigate a bit on-line. The internet has become wonderful way to quickly find peer reviewed literature. :)

One interesting 1998 study, perhaps relevant to aquariums, says:
"FeIIIEDTA has a half life of about 2 hours in sunlit waters. Complexes ofEDTA with other metals do not exchange with iron and are photostable. Therefore, EDTA behaves like 2 different compounds: - FeIIIEDTA undergoes fast photolysis with biodegradation of the metabolites. The other metal-EDTA complexes are persistent in the environment." Biodegradation of the photolysis products of FeIIIEDTA

While, the EDTA detoxification of heavy metals is stable (as mentioned by Diana), the resulting Fe complex is not....although 2 hours is much shorter than i thought. This info may be important for choice and frequency of iron dosing expecially in tanks wo soil. However, sunlight is much wider spectrum than artificial light. I believe the UV may be the culprit (organics are more efficient absorbers of short wavelenths), so 2hr may be an extreme value unless UV filter is used.

Then i got to think about my statement about HEEDTA and DTPA stability. These are the chelators used in Tropica's TMG/TPN which i have used for the past 15 years. One reference i found says they are indeed more stable at high pH, DTPA stability. I have not yet found anything about its photo-sensitivity, although Tropica says it can be dosed weekly and I trust what Claus has been recommending.

What about the stability of other iron additives, like ferrous iron (Fe+2) gluconate (i have never used it, but it seems to be needed daily?) and of other trace element products. CSM Plantex uses EDTA.

Are there other dry trace element mixtures which use better more stable chelators?
 

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EDTA will bind divalent cations, but I don't know how what the affinities for different cations are. While, I can't speak to the stability of Fe chelators, but I use DTPA chelated iron solution. I have hard water, and found adding EDTA-iron always brought on a precipitate. I don't see any precipitation with the DTPA.
 

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Hi, nfrank. DTPA chelated Fe at 10% concentration is available on most aquarium dry fertilizer sources (GLA/Orlando, Rex, etc). Additionally, I have been told but have not confirmed that Miller's Microplex uses DTPA as its chelating agent.

Using my eyes on and experience with plants as my testing kit -- the same method you discussed in Dummy Question #6 -- even with DTPA I find benefits from dosing daily, with better color (not necessarily shades of red) and leaf size and density forming with regular Fe and micronutrient addition. Though I do agree Tropica's Master Grow is the best micronutrient fertilizer I've ever used, I also preferred to dose it multiple days of the week. (I've never used Plant Nutrition.)

Last two cents is I've put DTPA chelated Fe into Seachem's Excel and dosed it to .2ppm Fe / 5mLs into 10 gallons and was very happy with it as my version of Special Sauce to perk plants up. Some input from our chemists about chelated Fe in a solution with glutaraldehyde is appreciated, though I'm sure fellow nerds are already googling, though most studies are in relation to Fe in blood/hemoglobin.

I have not yet found anything about its photo-sensitivity, although Tropica says it can be dosed weekly and I trust what Claus has been recommending.
Only so I understand/for my curiosity: does this mean you find Tropica's relatively low Fe addition in it's recommended dosages adequate for your tanks, or that you trust Christensen's recommendation but also dose more than the recommended doses in your sweet tank?

Thanks for the informative pdf, sorry about the messy post. Stop distracting me from work, APC, dammit.
 

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Bert H said:
I have hard water, and found adding EDTA-iron always brought on a precipitate. I don't see any precipitation with the DTPA.
nfrank said:
what DPTA product do you use, and how often?
Not exactly the same, but you guys might like these pics from an old demonstration I did on some other thread, especially in regards to time percipitate forms. The time indicated is time between DTPA chelated Fe input (what would be 0.5ppm Fe into my tank's volume) and KH2PO4 input (2ppm, same). The pic was taken approximately 5 minutes after adding KH2PO4 into each container. IIRC I bought this DTPA Fe from Rex.





 

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Discussion Starter · #6 ·
Only so I understand/for my curiosity: does this mean you find Tropica's relatively low Fe addition in it's recommended dosages adequate for your tanks, or that you trust Christensen's recommendation but also dose more than the recommended doses in your sweet tank?
QUOTE]

With my soft tap water (KH<2), and moderate additions of minerals (1t CaSO4, plaster + 1t Epson salt to 60gallons of replacement water), i have been dosing 45-50 ml TPN weekly. In older tanks, i recall that i dosed 20ml per 70gal. I believe both are less than Tropica's recommended amounts on the label. My tap water does provide some iron, and the AS might provide some. My previous tanks also had some iron in the substrate.

Once i stop playing with macros, i would be willing to experiment with adding extra Fe. I do prefer a product that does not have to be added daily.

The Iron - PO4 precipates are interesting. If i remember, i will try that with TMG. Precipates are not necessarily all bad, at least for the plants i like to keep The Fe can resolublize once it settles into anaerobic zones of the substrate. As we know, ferns however, depend on the water column. So, i have to beleive that i am maintaining high enough levels to keep them happy. I also have a nice crop of Riccia attached to the intake of my overflow.
 

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Discussion Starter · #7 ·
what DPTA product do you use, and how often?
I am still very interested to learn how often folks use DPTA chelated Fe.... and if anyone has done Fe tests to see how stable are the concentrations over several days or longer.

Apparently, this conversation occurred years ago on APC. For example, I found this. See HeyPK's Comments. I checked the product he mentioned and found it is still available. Iron DPTA

I looked at my Fert Box, and found i still have over a pound of 10% FeDPTA.

So how do folks use it, how much, how often? I am hoping it doesnt have to be used daily, and someone has data to demonstrate this :)
To dispense traces dry, this would be helpful: Pinch spoons. Similar dispensors come with aquarium test kits. I need to hunt for mine.
 

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what DPTA product do you use, and how often?
I bought a fairly large amount of it from Greg back when he had his on-line business. I use 2 ml of Flourish, and 1ml of the iron chelate on my moderately lit 50's 3-4x/wk. I've never known how folks can add the humongous amounts of iron they do and not have problems. I tried increasing the amounts for a while, but it seemed to correlate to an increase in gda. I can't see where my plants need any more than that. Maybe if I had more lighting, it might be needed.

I've never bothered to try to figure out how long it remains available.
 

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A couple notes for others that we missed in our discussion:

1) When I state that I have found it advantageous to dose Fe daily, I should also note that my tap has moderately high (~6dKH) carbonate hardness, which has an effect on the effectiveness of the chelator. Folks with zero/low KH and very acidic water/soil will find that has an effect on their needs for Fe input and quality of chealtor.

2) I grow lots of fast growers in every high tech tank I've kept, which, again, affects my tanks' Fe needs.

3) This discussion is about Fe specifically. This is worth restating because many people confuse Fe discussions with a discussion on all traces. For example, when we dose DTPA chelated Fe, we are not doing it as a replacement for, say, Flourish or Plantex or Microplex or whatever, but rather as a supplement to such a trace mix.

nfrank,

Did you see the Sprint 138, using EDDHA? From their papers:
Sprint 138, a 6 percent fully chelated EDDHA iron, is preferred inthe most challenging soils that are alkaline and calcareous,including soils with a pH greater than 7.0. Sprint 138 contains thehighest ortho ortho (5.2%) content available in the industry, pro-viding a highly efficient chelate that will keep working to "shuttleiron" from the soil to the plant for an extended period of time. Soil Application
But pricey at ~$20/lb in 5lb quantities for a lower percentage of Fe. But, of course, if it stays available for a very long period of time...
 

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Discussion Starter · #12 ·
"WET" provides good summary and reminder points:
1. stability of chelated Fe may be lower with higher alkalinity (test results talk about pH, but that may be indicator of KH)
2. Uptake of Fe is likely higher with fast growing plants. That can explain why i get away with lower iron levels, even with TPN.
3. Balanced inclusion of other trace elements are also important.

I googled and found a few papers that indicate that EDDHA is even more stable than DPTA with high pH. http://extension.unh.edu/agric/AGGHFL/pHarticl.pdf. This publication pointed out "if a different nutrient (e.g. manganese) is limiting then application of iron may worsen the
problem because of antagonistic effects."

I couldnt remember why i dont specifically do iron supplements. Are folks really conviced that iron alone is lacking. I would much prefer a complete suite of trace elements, in the correct proportion, but one with a more stable, less photosensitive chelator which doesnt require daily dosing. If Fe is the problem trace, then a mix of FeEDTA (with other traces) supplemented with FeDPTA may make sense. There used to be powder which came that way.EDTA+DPTA mix I think Microplex (4%Fe)and Plantex(7%Fe) both use EDTA. So, a mix of Microplex and DPTA Fe? (provided that you wont miss the copper)
 

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nfrank,
Are folks really conviced that iron alone is lacking.
I find this a particularly good question because, as you know, measuring available Fe in soils and the water column is impractical for us hobbyist farmers. Zapins made a good point in General the other day suggesting the reason a guru (we all know) claims CO2 the root cause of most any plant problem is that, due to the lack of available testing equipment, it is an unproveable claim. While I disagree with Z about that particular guru's motives, I do acknowledge that much of this -- CO2, COD, Fe, and so on -- is a little close to voodoo and relies a little too much on anecdotal information. Voodoo in the same way that, say, guys will justify dropping thousands of dollars on audio cables because, hell, they hear the difference. F logic.

But to answer your question, I am convinced that Fe is a nutrient that needs special attention. I realize the better color (green plants are greener, red plants redder) I experience is entirely subjective. I realize I've no hard data. But Fe is an easy variable to control with easily available fertilizers and the many times I've played with the variable only strengthens my conviction.

I also think, like anything in this hobby, we should all try for ourselves and hope others share what they find. The funnest part of playing with Fe is changes show impact relatively quickly, and we can play with quantities or frequency for, say, 1-2 week samples and clearly see the (lack of?) effect on our fast growers. And our plants can recover from mistakes just as quickly.

I would much prefer a complete suite of trace elements, in the correct proportion, but one with a more stable, less photosensitive chelator which doesnt require daily dosing.
How important is this lack of dosing to you? I realize you've automated your water changes, but would you be willing to keep an extremely acidic 0 dKH tank if it meant nutrients such as Fe stayed available? In addition to the other benefits acidity gets us with certain plants, of course.

If Fe is the problem trace, then a mix of FeEDTA (with other traces) supplemented with FeDPTA may make sense. There used to be powder which came that way.EDTA+DPTA mix I think Microplex (4%Fe)and Plantex(7%Fe) both use EDTA. So, a mix of Microplex and DPTA Fe?
You may be interested to know that back in 2004 Greg Watson had the same idea. He released a mix called "Plantex CSM+B+Extra Fe" which, using additional DPTA Fe, increased the percent of Fe from Plantex CSM+B's standard ~7% to ~10% by mass. Gains from this product got me interested in Fe as an individual nutrient! The special mix never took off though and Greg discontinued it within months. You may find it humorous that I still have and occasionally use some of that original batch and add fresh chelated Fe because I know that original batch's Fe has long since oxidized. There have been periods over the years where the bag got a hole and was exposed to oxygen, I kept it in a clear container out in sunlight, and so on. :D
 

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Discussion Starter · #14 ·
Your provided empirical evidence is strong.

I can try to offer a rationale why extra doses of iron may in fact be needed, and not the other traces.... even for lower pH and KH. As i indicated in my initial post on this topic, the Fe-EDTA bond may be weaker than the other trace elements. So, additional doses of iron may make sense.

How important is this lack of dosing to you? I realize you've automated your water changes, but would you be willing to keep an extremely acidic 0 dKH tank if it meant nutrients such as Fe stayed available?
I am a creature of habit.... and it is hard to teach an old gardener new tricks! I really like weekly dosing of traces.

I do keep my KH very low. My tap water only has 1-2 deg hardness, and i only add 1t CaSO4 + 1t Epson Salt (MgSO4*hydrate) with each 60 gallons of replacement water. KH probably stays very low. I havent calibrated my pH probe in a while, but believe the pH is in the low 6's. However, I am not sure pH is the only issue with EDTA. The lit suggests it is also photo-reactive. Of course, i havent tested for Fe variation. Data would be handy.
 

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I am no scientist but I will put my .02 in here. I have a high tech tank and have not been dosing Fe by itself for the past week or so because I ran out. I was only dosing CSM+B. On Thursday I started putting seachem Fe in the tank again and I can say that visually the tank looks much healthier. I was under the assumption that the Fe in CSM+B would be enough but it seems that is not true in my case.
 

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From the link posted by bigstick
Ingredients include purified water.
"Iron (min) 1.2% "

I would rather not pay that much for water...
 

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What we know about EDDHA chelated Fe (Sprint 138, aka "Super Iron")

6.0% EDDHA Chelated Fe. The label looks like this:


It is a very dark substance that will stain the water. The left is a large (~1.0ppm into 20 gallons) wet dose and the right the trial/experiment sample of dry. I am sorry for the cellphone pics. I'll update these images this weekend if you'd like.


Weight trials (10) for 1 leveled teaspoon (5mL) show a density of 2.42 grams per 5mL.

Trials (scale accurate to 10mg)
2.42g
2.42g
2.43g
2.42g
2.42g
2.42g
2.42g
2.42g
2.43g
2.42g

So,

about 1/8tsp adds 0.2ppm Fe into 25 gallons.
about 1/16tsp adds 0.1ppm Fe into 25 gallons.

At 0.2ppm Fe it will color the water pink. Certainly gets your plants redder looking ;) ... an optimist might call it a free 9325K effect ;) :D This video is currently being processed by YouTube but has a test of 0.2 ppm Fe into my tank. It still retained a pink tint ~12 hours later.

Dosages at 0.05ppm do not noticeably cloud the water.

I am going to continue to experiment with this chelator. However, the side effects probably mean we have to use it at a low concentration, which may mean it can only be a supplement to other sources of Iron. For example, Tropica uses some percentage of DTPA and HEEDTA in their solutions, and Tropica Master Grow is a pinkish purple that does not noticeably tint the water column after 5 minutes of dosing. I can continue updating in this thread if there is interest else I'm sure I'll post about it in whatever threads it is relevant in :)
 

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Discussion Starter · #19 ·
Very impressive documentation.

As we discussed off line, folks on other forums have also reported the staining effect of FeEDDTA.

This is not to say that this product does not have value as a supplemental source of Fe as WET mentioned. First, it could be useful when used at the concentration that does not cause discoloration. This may be consistent with Tropica's mix of DTPA and HEEDA which i have heard is mostly DPTA. Second, the discoloration can be an indicator of how long it stays in solution. Until the color dissapears, the Fe-EDDTA iron levels may be present. However, this can also suggest that the plants are having trouble consuming it.

Additional dosing tests may be useful, to reflect differnt several environments: (1) high light and minimal or no plants (to look at photosensitivity), (2) high light and large plant mass (to look at incremental rates of plant uptake), probably with and without other consumable Fe and (3) at different levels of GH (to reflect pH without CO2) to judge differential stability.

Until i know more about (1) and (2), i am not going to put it in my "show" tank. :).
 

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let me apologize ahead of time for any typos as I peck at this phone ;)

I misunderstood what you found elsewhere - I did not know anyone had used eddha in an aquarium before but understood the staining that comes with certain chelators such as (possibly?) heedta. is that right or got linkage?

1) will be easy with a sample in a cup. 2) can be my tank and anyone with high light testing (and I hope you're still down with some other tank). 3) should be kh? this is a great set of initial tests that we can build on!

this weekend will involve massive water changes and testing for a good range from eddha, after I see what happens with the current dose. (I've not checked since leaving home this morning, of course.)

thanks neil.
 
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