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Re: Fe2+ / Fe3+ [long but hopefully interesting]

> Date: Mon, 20 Apr 1998 18:00:35 -0700
> From: Stephen Pushak <teban at powersonic_bc.ca>
> I think we assume that most of the iron used by rooted, mature plants
> comes from the water when we have a laterite or iron containing
> substrate and are adding PMDD or Dupla daily drops or something similar.
> Is this assumption justified??

I tend to assume that stem plants get a lot of iron from the water since the 
roots are removed during bi-weekly pruning.  They do tend to regenerate a lot of 
root mass quickly, but I have to think that a lot of iron is coming in via the 
leaves for at least a few days. 
This assumption may be true for massively rooted plants like crytps that aren't 
typically uprooted for pruning.

> Later on in the article Kasper summarizes the function of laterite in a
> section titled "The tasks of Duplarit in an aquarium". He says:
> "Duplarit (laterite) performs a similar task in the aquarium as in
> tropical regions. Under slightly anaerobic conditions in the aquarium
> substrate as well as through the plant root' active dissolution of the
> substrate's iron (through the escape of plant specific organic acids)
> the nutrient absorption through the roots is provided with sufficient
> nutritional iron."
> On George's Aquatic Concepts web pages now found at
> http://www.cco.caltech.edu/~aquaria/AquaticConcepts/ he discusses
> several of the functions of heating coils. He says that [heating coils]
> "Provide warmth in the substrate to speed up biochemical processes." 
> [snip] 
> I told Neil Frank I thought heating coils might be helping provide iron
> in George's laterite substrates and he countered: "I don't buy this....
> maybe he can test it out by not using his daily dupla drops which is
> essentially only iron." This is a reasonable experiment and maybe George
> could try it for a few weeks.

Oh, sure, not adding Dupla drops for a few weeks is VERY reasonable.  Let me run 
right home and start killing my plants. Good idea Neil. Note the lack of a 

To my fevered brain, and as clearly stated on my website, the heating coils are 
MAINLY there to create circulation currents which pull the chelated iron from 
the water column into the substrate where it is bound by the sufficiently high 
CEC of the laterite until it can be adsorbed by plant roots.  If the warmer 
substrate helps with other chemical processes or with delicate plants, that's a 
bonus not a design goal. 

I have no doubt that the laterite provides lots of iron initially (the first 
month or so after setup).  I typically measure iron levels in the water of 0.5 
mg/l or more right off the bat.  After the tank is established, I only see lower 
levels corresponding to the addition of drops. I once measured iron levels right 
after a particularly brutal uprooting and pruning where the water was clouded 
red for a few hours. No spike in iron concentration as I would have suspected. I 
think there is some available iron in laterite but most is "locked up for life" 
in strong bonds with other minerals (of course, that's purely conjecture).  

I think the long term purpose of laterite in the substrate is to act as a 
bonding site for nutrients brought into the substrate by whatever circulation is