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Discussion Starter · #1 ·
Hi!

Is it true that the iron present in traces & chelated through EDTA process will be lost in case of exposure to light? A lot of people sugggests that the EDTA chelated iron should be dosed only after lights out.

Looking forward to comments.
 

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good point...I never thought of it, as I didn't know the process used is EDTA. I use the straight up Fe+++ will have to check
 

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Yes, it is lost from the water column due to photodegradation of the EDTA followed by precipitation of the Fe+3 (after oxidation from Fe+2). It's stilll in the aquarium - most likely in the gravel and filter.

The effect is most pronounced with wavelengths less than 400nm (UV) - thus the suggestion that a UV sterilizer not be run 24/7.

Fe+3 is a stronger chelator than some of the other trace elements needed by plants (like Co+2), so there is also a domino effect where the Fe+3 can "steal" an EDTA from a cobalt ion.

This paper: Laan et al, Environ. Chem. 2004, 1, 107-115. proposes a possible photostable, iron-binding-specific alternative to EDTA: desferrioxamine B. They showed that the compound is not photodegraded, but did not investigate the toxicity of DFO-B or its effect on the availability of the iron for plants (though they imply the data is being collected).
 

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Discussion Starter · #4 ·
Thanks Kevin for your reply. So what procedure do you follow? Do you dose your traces after lights out?
 

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good info Kevin...
I would think night dosing would alleviate this.
 

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No, I don't wait until lights out. I've become quite the lazy aquarium keeper. Fortunately, my plants don't seem to care . . .

I dose my micros once a week after a water change - usually 3-4 hours before lights out. My lights are 6700K T8's, so not much emission below 400nm anyway - I'm also not "super high" light - only about 3WPG equivalent.

I also only dose my macros once a week - also after the water change (though I wait about 30min between the two) - like I said, kind of a lazy aquarium keeper.

FWIW, the article claims a half-life (time until half the Fe-EDTA complex is destroyed) of 6.1 hours under cool-white fluorescent tubes at 150 micro-Einsteins per square meter-second. I am not familiar enough with the units to speculate how this compares to aquarium lighting though.
 
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