Why do you think that excessive iron in the water will kill everything?
CSM+B, a powdered trace element mix, and powdered iron chelate are available so cheaply I don't see any reason to concern ourselves with having good amounts of iron in the substrate. Plants take up nutrients through the leaves as well or better than they take them up through the roots.
I think saying that all plants take up nutrients in their leaves as well as or better than through the roots is way off. Underestimating the role of roots is all too common it seems.
Even plants with smaller root structures can feed rather heavily from their roots. Root size is usually more relative to anchoring, in aquatic plants.
A nutrient rich soil(from ada, mts, or other root nutrients) helps to provide a stable gap free source of nutrients(i get that EI does this too). Some nutrients are more easily taken up by roots, as well.
"Too much" of anything, including water and oxygen, is toxic. The amount of iron we can reasonably get into tank water is not toxic.
This. In fact, you're much more likely to have a deficiency than a toxic level.
Has anyone ever had a documented case of copper poisoning in inverts due to fert dosing? Other than copper based meds I am not sure anyone has ever actually harmed inverts with copper, yet we see questions on it all the time.
These are about the same as the people who don't understand why they have algae with 200 watts of t5ho lighting on there 29g tank.
To make a long story short. A long time ago I was a volunteer at the Baltimore National Aquarium. I brought some red clay in and they analyzed it with a machine they called an atomic analyzer. No Iron was detected even though it was red in color.
And this. Red does not mean high iron. Having worked with some high iron substrates in the development of RM, I've sampled a lot of commercially available natural red clays and have found most have essentially nothing but highly degraded nutrient devoid dirt in them.