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[APD] Re: Chelators

>> Sounds much more like some other problem than poor iron, Mg could have 
>> been the issue.GH could have changed in the tap etc, I've never associated 
>> a low Trace iron level with BGA. I've had RFUG's for 10 years with plants. 

>Hmmm, the tank is filled with well water that has very low KH and GH, so it 
>is supplemented with pulverised dolomite. Annual water tests done by the 
>local health department show no change in GH, and neither do my more frequent,
>but more crude, home tests.

Annual test? Hehe..........
Generally the home test are okay for GH though.....

>> I've had RFUG's for 10 years with plants. 

>Were you using Fe-gluconate or Fe-EDTA? 

I've used both and DTPH(Tropica)
Some very subtle differences and mainly Cu I believe rather than Fe chelator.

>>> Would Fe-gluconate be oxidized morerapidly than Fe-EDTA in the
>>> oxygen/bacteria-rich substrate of an undergravel filter? 

>>I would not think it would matter as far as the plants are concerned. 

>Well, then I'm baffled.  The only change I have made was to switch the 
>Fluorish with Fe-EDTA (whatever brand is cheapest at the time).  

Any particular species of plant that was effected and some that were not?
What type of substrate also?

>continued dosing with KNO3, Flourish phosphorus, and Flourish Trace.  
>I initially switched to a product that has Fe and K, but not Mg, so I 
>don't think I can attribute the problems to Mg deficiency.  The improvement 
>was so rapid that I am convinced of the causal link.  I just don't know WHY.

If it was rapid, then this sort of says that it was not traces, but rather something else.
Traces take a while to show up in plant health, I give them 3 weeks vs one week for macros before deciding.
You can see PO4 differences in less than hour if there is strong limitation.

>Oh well, the tank looks pretty good now, so I guess I won't worry 
>about it.


Well, if you are happy, stick with it.
Go back later if you are really curious and try to reproduce it for the reasons/assumptions you believe to be true.
See if they are, then decide.

Tom Barr 
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Aquatic-Plants at actwin_com