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[APD] trace element problem. Solved?

Hi All,

Last week, I posted a question about persistent chlorosis in a wide variety 
of plants.  The problem had persisted for months, despite regular addition of 
fairly large volumes of Flourish and Flourish Iron, and necessitated regular 
replacement of stem plants which died.  

I had suspected that the iron in the Flourish was, for some reason, 
unavailable to the plants.  So, for the past week, I have using a product 
containing iron chelated with EDTA rather than gluconate.  I have continued 
to dose with Flourish Trace and KNO3 as usual.  The results are startling.  
Rotala indica and a stunted amazon sword have greened up nicely.  Hygrophila 
difformis has started producing large, highly dissected leaves instead of 
small leaves similar to emersed growth.  

My best guess is that the bacteria in the undergravel filter were digesting 
the gluconate in the Flourish and allowing the iron to precipitate before the 
plants had a chance to use it.  Presumably, the EDTA is less affected by 
bacterial action.  Does that make sense?

Nicholas Plummer
nickplummer at att_net
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