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Re: Actinic lights and algae problems

On Mon, 14 Feb 2000, Greg Morin wrote:
> Based on Roger Miller's comments to your original post it appears to 
> me that the main concern here with this reaction is that EDTA bound 
> ferric iron will be reduced to release free ferrous iron (in the 
> presence of strong actinic lighting), thus yielding a source of iron 
> very readily used by algae.
> Since we are still selling quite a lot of Flourish and Flourish Iron, 
> I would have to conclude that people are not having massive algae 
> outbreaks using these products ;-).

I don't find that too surprising, whether we're using ferrous or ferric

Taking a step back for a second to the approach that Ms. Walstad's is
promoting, she uses fish food as the major source of plant nutrients and
she feeds heavily.  She (on pg. 160) reports phosphorus levels in her
tanks at 1-5 mg/l of P (that would be about 3-15 mg/l of phosphate) and
says "it's highly unlikely that phosphate deficiency would ever limit
algal growth in the typical aquarium."

Given those phosphorus levels I'm not surprised that algae in her tanks -
or other tanks of similar construction - might be hypersensitive to small
amounts of iron.  With phosphorus levels that high, iron is far more
likely to be growth-limiting then phosphorus; any small addition of iron
might translate directly into algae.

Judging from past discussion on this list it sounds like most of us
probably have atypical aquariums(?!) with far lower phosphate
concentrations than Ms. Walstad's.  For most of us, phosphorus is much
more likely to be limiting than is iron and we might happily add quite a
lot of iron (ferrous or ferric) without seeing any sudden explosion in
algae growth.

This is one of those points where Ms. Walstad appears to come to a
perfectly correct conclusion that's really only meaningful if you're using
her methods.

Roger Miller