UV and Fe Dosing

Frank Lawler

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Apr 15, 2009
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I have read that a UV sterilizer can cause Fe to precipitate, making it unavailable to plants. Is this true? I had been running my sterilizer 24/hrs day, but just cut it back to 10 (same as photoperiod).
I am trying to raise my Fe from 0.4 -0.6 to about 1.0 or more to see if I can get some red in the Rotala Macranda. Thanks.
 

Philosophos

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I haven't seen any evidence for it. I'm not sure of the physics behind it either.

I'm kind of wondering how busting off the chelate would alter your testable iron levels, Oreo. You typically need a nuclear reaction to make iron not iron anymore. Without the chelate, you'd just wind up with iron oxide which is exactly what a test kit should be able to read.

Red isn't dependent on iron more than say potassium or phosphorous. There's no iron to be found in anthocyanin or chlorophyll, which are directly responsible for red and green. Nitrogen limitation is the place to look, that and Carbon of course.
 

Oreo

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May 6, 2010
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If it precipitates it can be settled or filtered out. I don't really understand how it works either but the numbers don't lie in my case. Granted, my case may not be the norm considering the very high UV exposure I'm using.
 

Oreo

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Is there any way I could help you guys with testing this particular issue? I'm already set up for it really well. How / what kind of test would you like to see run?
 

Philosophos

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The precipitates settling is a possibility, but identifying UV as the cause is hard with all of those variables. Even an above-neutral pH makes EDTA break down fast, and gluconate is lucky to last 24 hours in any tank. I also wonder how much that even effects things given the CEC most of us have in our substrate. That's a question for later though, I guess figuring out if it's happening would be the first important step.

It would be handy to find out what atomic theory has to say about using UV to bust the two iron atoms off of the chelate. Making theory and practice match would be a good first step. Personally, I've got no clue how to figure that out.

I'm guessing testing EDTA would be the most useful. Not the easiest though since it seems to disassociate rapidly at neutral pH. You could either use controls and subtract or do some fancy bits with acids to keep it holding together for longer.

Now testing for it wouldn't be so hard. Shouldn't it just be a matter of dumping a known quantity of iron chelate through various exposure levels of UV sterilization then using EDTA and Eriochrome Black T to pull off a titration test? The less EDTA for a color change, the more is still bonded. Toss in some controls and away you go.
 

Frank Lawler

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A tank filled only with water could be dosed with Fe, then tested. Might want to test for a few days to get a sense of the non-UV levels. Then put in the UV sterilizer and see what happens.
 

Oreo

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Frank Lawler;50904 said:
A tank filled only with water could be dosed with Fe, then tested. Might want to test for a few days to get a sense of the non-UV levels. Then put in the UV sterilizer and see what happens.
That's kinda what I was thinking. I mean it would be nice to investigate the mathematics & chemistry behind it all but a yes / no test can be that simple
 

Philosophos

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Eriochrome Black T + EDTA = hobby GH test kit ;)

You can get your hands on both easily, or better yet just calibrate a test kit.
 

Tom Barr

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I think several reported the residual Fe is removed fairly quick with UV.

But does this effect growth much if you dose often?
Does not appear so IME.