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Re: Hair Algae and Iron


On Sun, 26 Dec 1999, Tim Marks was concerned that hair algae appearing in
his new tank might be caused by too much iron.

Tim really didn't provide us with much information to answer his question.  
However, regardless of what might cause the hair algae, Michael Rubin is
certainly right that if Tim suspects iron then he shouldn't add Flourish
Iron.  Also, I think that Karl Schoeler's advice on controlling the hair
algae without changing the fertilizer regime was right on.

Tim's original question and Sylvia's response that iron fertilization is
correlated in her tanks with hair algae outbreaks brings up an interesting
point.

A couple months ago I e-mailed a note to a biology professor at the
local University, asking if dissolved organic carbon released by stressed
plants could feed algal growth.  In his reply he indicated (among other
things) that he expected either phosphorus or iron to control algae growth
in an aquarium. Further, folks using PMDD have testified repeatedly that
iron levels over 0.1 mg/l can cause hair algae outbreaks (as an aside, if
high iron can cause algae outbreaks in a tank fed with PMDD, then
phosphorus is not the limiting nutrient). To top it off, Diana Walstad in
her new book argues strongly that low iron concentrations can be an
effective control on algae growth.

I've pretty much bought into the idea that I need to keep iron low to
control algae growth, and I do that by adding iron mostly to the
substrate.  What I don't understand is why algae outbreaks seem to require
more that 0.1 mg/l of iron; given the low concentrations of iron in plants
and algae, it seems like far less than 0.1 mg/l iron would be required to
promote growth.

Diana Walstad asserted that algae need dissolved, uncomplexed iron for
growth. This is unlike plants that can use complexed iron and scavenge
oxidized iron from the substrate.  Is it possible that all the efforts to
read and control chelated iron in solution are actually irrelevant to
algae control?  Maybe what all you iron testers need isn't a kit that you
can use to indicate moderate to high levels of chelated iron, but a kit
that gives very sensitive (say, under 0.01 mg/l) results for dissolved,
uncomplexed iron.


Roger Miller