Diane Walstad talks about CO2 limited tanks where growth and plants demand is very limited compared to your high tech tank. When there's high growth iron fertilization in the substrate is probably not enough.
I never starved my plants on CO2. Co2 is in the range of 30 - 35 ppm here
I feed the plants iron from the column I say that aswell, plus the fact that I notice that the plants suffer when there is not enought iron in the column, thing is that there is no iron at all on my substrate.
The fact that Walstad speaks of no CO2 injected tanks makes no difference in relation to the fact of where from preferably plants aquire their iron (roots or leaves) or the fact that if iron is aquired from the substrate then there will be no iron for the algae to use in the water column at least not that much. My problem is that enough iron on the column here brings algae.
I have no UV installation I speak of the UV emited from the MH lamps.
If you notice Walstad states that UV breaks DOC binded iron back into it's free form. And this is what I wonder that may be happening.