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[APD] Re: Aquatic-Plants Digest, Vol 16, Issue 3

>They aren't magic compounds that do all sorts of wonderous things, and despite most of us having strong >science backgrounds none of us are experts on iron transport in aquatic environments. 

Jeff, you have to _believe_ in the magic for it to work:-)

>I don't even think Tom has looked as these chemistries in much detail, his livelyhood is in this area. 

I wish I could agree with you. I unfortunately have looked into it in great detail. 

>In other words I think we're fooling ourselves if we think we understand any of this - the devil is in the details, >all the factors that effect iron availability are way too complicated to distill into some amateur theory - there is >pH, dissolved oxygen levels, substrate interaction, humic compound interactions, and on and on, and lastly >chelation. Iron is involved in all sorts of very complex equilbria, even without a chelating agent, I don't think this >discussion is helpful or relevant.

In general, yes.
Redox controls a lot of it. pH/O2/Organic matter loading rates/humics are the main factors. 

>The reason I mention this as that I don't think it matters, the problems people are seeing are likely light and >CO2, in some case macronutrients, in even fewer cases problems with traces unless they are not adding >enough.

Yep, agree 100%.

> This is the important point - Until someone actually does a controlled experiment, all of this discussion is >worthless - its too complex to theorize. Wu from the DFW club now is switching the iron sulphate, no chelating >agent and I would not be suprised if he reports absolutely no change in his tanks, I'm eagerly awaiting his >results.

I used iron filings.
It worked well.
Flourite does work better than sand laterite or dosing the water column exclusively.
I do not think we are unable to get some useful infomation out of this though. 

You can isolate Fe and it's various chelators also.
There are micro's that have everything EXCEPT Fe.
There are several products that have only Fe and different Chelators(or none).

We can add the other nutrients to non limiting levels.
Then reduce the dependent variable(Rust, Fe ETDA, or Fe gluconate etc) down to "limiting" levels slowly and use plant health as our gauge ...since... that is the indicator of interest and the goal of aquatic nutrient horticulture.

We can use plants as the indicator.

While plant species will have specific needs and respoinses, a general trend can be determined with a plant community. I know some plants are fine with little Fe added to the substrate while others will do better. I know this from doing a controlled RFUG without any substrate Fe. 

I've used DTPA, ETDA and Gluconate.

Whether or not the Fe chelators causes any differences, I cannot say. Are they significant differences? I doubt it.
Why? It takes little energy for the plant to reduce or remove the Chelator and the AMOUNT of Fe is very small against say, Nitrogen. 

Given these factors, I think it'll be very tough to show any significant differences vs something like having good consistent CO2.

Ca++ is another completely different issue.  

The other issues are also Mn chelators, Cu levels(Fe and Cu use the same transporters in many plants), plants(grasses) also can produce their own external chelators when needed.   

While these are somewhat complicated, they are not unattainable to find out our questions........eg , "does it work and how significant is it in practical aquatic plant health?"  

Tom Barr


Light spectrum, substrate heating, substrate composition, trace element mix, I don't think that any of what I just mentions matters at all. Making a big deal of out stuff like this because we think we know what we're talking about,

1) scares newbies away and removes the focus from the important issues, light and CO2, secondly macros, thirdly and lastly, stuff like trace mixes

2) discourages experimentation because people think you need to do it a certain way, because XYZ who posts an awful lot said so. So much of our hobby is based on bunk info that got printed once and then re-cited through the years... (see the dump-and-squirt method of acclimation for an example of this, phosphate causes algae, etc) Do the experiments! Have fun! There is no one way.

K.I.S.S., Occam's Razor, Bayesian Inference, it has many names but lets not make it overly complex without the facts to back it up. :)

Jeff Ludwig
Elkton, MD

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