[Randy Holmes-Farley]

EDTA is known to natural waters chemists and biologists as a way to reduce potentially toxic metal availability to levels where they can be studied.

What is it that you want to accomplish? Copper and iron and certain other metals do need to be bioavailable. It is not apparent to me that it is present at excessively high levels in my tank, at 0.01 ppm copper. Adding a lot of EDTA might not be a good idea if it reduced bioavailability a lot.

Also, we have magnesium and calcium at vastly higher concentrations than copper. For magnesium, it is 340,000 times as concentrated as copper. I'm not sure the equilibrium binding of copper to EDTA is enough stronger than to magnesium and calcium to allow all that much copper binding (but this could be looked up), especially if the copper is already bound to organics (as it is in seawater).