Thanks guys for taking the time to share your thoughts
From my own personal experiences, I know for a fact that if miss two consecutive water changes, algae will appear & may take a month to disappear.
I think that the above could perceivably be used as evidence to support the supposition that
disproportionately (and the key word is "disproportionately") large water changes, typically 50% or more, advocated as part and parcel of eutrophic dosing methods such as EI are to reset nutrient levels, to prevent build up thereof, and the subsequent imbalances that can kick start algal blooms, for instance.
I believe that plants (maybe not all) do secrete substances other than O2. Chemodefence against predators or even agaist other plant competitors is a common thing in natural ecosystems.
Undoubtedly, they also remove the toxic substances of fish respiration as well, but as for plant secretions, I am afraid I remain very sceptical. I doubt that even under accelerated photosynthesis substances such as allelochemicals will be produced in sufficient quantities to impact on an aquarium, especially in the space of a week or so.
Further, it is possible to tweak EI to a point where the input of nutrients can be reduced to a minimum whist still providing non-limiting nutrient availability to plants. This in turn means that you can reduce water changes from say once a week to once every two weeks or more. Surely this is further evidence that the
disproportionally large water changes are to reset nutient levels and not to remove the toxic products of fish or plant metabolism, should the latter exist? If they were to remove toxic products of metabolism wouldn't a weekly water change, of say 15% to 20%, be sufficient?