Re: [APD] Re: Iron and UV -- or - Reducing problems

["S. Hieber" <shieber at yahoo_com>]

I've never had any Fe shortage showing up in my plants on
tanks running UVs 24/7. I've watched APD for several years
for any evidence of plants showing Fe shortage attributable
to UV and evidence is scant to say the least. I've even
tried dosing large amounts of Fe with the UV off to see if
I was simply missing seeing something -- but no. I've even
spent the bigger bucks for a high quality Hach iron test
kit to see if I could find an Fe problem, but no.
Apparently, even if photoreduction breaks down the
chelators and thereby allows the iron to oxidize faster
than it would otherwise, the Fe is still in the aquarium
and the plants can still make use of it. Tom Barr and Dr.
Greg Morin have added a lot to the discussion on this
topic.

As for reasonably affordable iron tests, I've concluded
that they are as Samuel Goldwyn once said of verbal
contracts, "not worth the paper they're printed on." ;-)
They are perhaps the 2nd-most notorious of unreliable
tests, after CO2 test kits.

Some kinds of reasonably affordable test kits are usefully
accurate. For Fe, watch your plants, not the test.

Scott H.
--- Michi Henning <michi at zeroc_com> wrote:

> I run a sterilizer as well, and I'm seeing the same
> thing. Add traces,
> and I get an Fe reading and, a few hours later, I read
> zero again.
> 
> I came across a suggestion some months ago (sorry, I
> can't remember where)
> that the UV is responsible. UV destroys the chelating
> agents in the
> trace mix, so the iron atoms are no longer surrounded by
> a protective shell.
> That allows the oxygen in the water to oxidize the iron
> and turn it into
> Fe3+, which plants can't use (they want Fe2+ instead).
> 
> I just did a quick browse on the web and came across this
> link, which
> supports this idea:
> 
> http://www.clemson.edu/hort/sctop/bsec/bsec-04.htm



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