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Re: [APD] Excel and U.V. light

>          U.V. light causes a lot of chemical bonds to break down. As I
>understand it breaks down "chelation".
>          The reason for adding Chelated compounds to the aquarium water is
>to prevent the wanted metal from being oxidized rapidly and unaccessible to
>the plants. A chelated compound breaks down slowly and releases the wanted
>form of metal over a longer time. Thus benefiting the plant.

Chelates (such as EDTA) are very stable under typical aquarium 
conditions and do not degrade at a rate rapid enough to provide any 
meaningful level of iron in this manner. The method by which plants 
extract iron from EDTA is when the EDTA-iron is pulled down into the 
root zone where the pH is much lower and thus conditions are 
conducive to extraction of iron by the plants directly as it is 
released from the chelate under the acid conditions or the plants can 
also utilize phytosiderophores to extract the iron directly. However, 
in the water column there is no release of iron (-> insert shameless 
pitch here - use Flourish Iron to target leaves, stems as well as 
root zone - it is non-EDTA based).

>          U.V. light would break down the compound (& chelated nutrients)
>rapidly and thus exhaust it quickly.

This would make sense, the chelate would rapidly release the iron which would then rapidly fall out as iron oxide, thus rapidly removing all of it from the water column so it could no longer resupply the root zone with this iron source. Eventually the precipitate would work into the root zone but it would take awhile.

-Greg Morin
Gregory Morin, Ph.D.  ~~~~~~~Chairman/CEO~~~~~~~~~~~~~~
Seachem Laboratories, Inc.      www.seachem.com     888-SEACHEM
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