Thanks so much everyone for your thoughts. Maybe EI is not universal, but lots of people seem to be using it with great results. So my question is not whether it works, but why. When CO2, light, and ferts are within certain parameters (for which we seem to now have a pretty good feel), one starts with lots of healthy plants, water is changed regularly and organics are low, plants thrive and algae all but disappears. Why? It’s not for lack of space—algae could grow on the glass, wood, leaves, water column, etc., but it doesn’t. Why? Raising NO3 and seeing BGA disappear is correlation, not causation. NO3 is not toxic to BGA, right, I mean, it needs N too right? Same for PO4 and GSA, e.g. I’m sure GSA likes PO4, and if we were trying to raise GSA we would need some P in the mix somewhere, right? Adding these ‘algae foods’ will not in itself make algae go away. So what is it about these ‘magical’ parameters we use that favors plants over algae? I can only imagine 2 explanations--either:
(1) abundant healthy happy plants under ideal parameters outcompete algae for a particular nutrient that it needs, e.g., given everything else it needs in unlimited amounts, plants are better than algae at capturing PO4. but as dark cobra says, if PO4 is not really limited either under EI, how can there be competition?
(2) abundant healthy happy plants under ideal parameters release some sort of allelopathic chemical that inhibits algae. Identify that and you stand to make some money!
or something else we have not yet imagined..intervention from Poseidon?
Thanks for amusing me here; I’m just the sort of person who wants to know why.