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> From: eworobe at cc_UManitoba.CA
> Date: Thu, 20 Mar 1997 07:39:22 -0600 (CST)
> Subject: Re: EDTA

> EDTA breaks down in the presence of light, no matter what cation is 
> complexed with it. This is because, like most organic compounds, EDTA
> is degraded in the presence of UV light. To suggest that sodium EDTA is 
> somehow safe from this process is ridiculous, especially since Na will be 
> displaced from EDTA in the presence of Fe or other cations.

1.  The rate of degradation is related to what counterion is present.  
Fe:EDTA is much more vlunerable to light and oxygen exposure than pure 
sodium EDTA.

2.  Stock solutions of pure sodium EDTA salts are reasonably stable in the 
light.  That's what I said.  Fe:EDTA isn't.

If an aquarist thinks that a solution of Fe:EDTA will be stable in the 
light for a year, they are in trouble.  If someone were to put pure Na:EDTA 
in a clear glass bottle for mixing with a trace element supplement later, 
and came back in a year, the solutions would be fine for making trace 
elements.  That is the bottom line for aquarists.

Maybe you would like to chip in some absurd comments on the color of pure 
water as well.