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Re: Actinic lights and algae problems

The threshold concentration (0.1 ppm Fe) mentioned for Fe is a "funny"
number because it is a test kit number not an absolute number based upon
regular complete water exchanges using a made water of known
composition. It corresponds to what the manufacturer calibrates the test
kit to using a particular prepared concentration (a calibration
solution). The calibration could be done in a low oxygen, iron sulphate
solution, or in a solution of Fe-EDTA or DTPA or a combination of both
or other synthetic chelators. These synthetic chelators are much
stronger than the natural humic compounds and thus the iron is less bio
available. This may be why the concentration of iron can be so high
(0.1ppm) without apparent algae problems when using COTS (comes off the
shelf) products. I disagree with an hypothesis Diana made in private
discussion (I don't know if its in the book) that increasing free
chelant concentration in water should decrease bio-availability of Fe. I
think its the other way around; more chelants = higher bio-availability
assuming that there is a source of reduced Fe in the system such as the

There are some references on my website about Fe uptake mechanisms that
apply to foliar uptake; plants use both Fe reductase to break the
chelating bond and can absorb chelated Fe directly. I'm too lazy to look
up the full details right now. Check it out if you are curious.
Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!